1

Hypoxia, Fetal & Neonatal Physiology:

100 years on from Sir Joseph Barcroft

1D A Giussani, 2L Bennet, 1A N Sferruzzi-Perri, 1O R Vaughan & 1AL Fowden

1Department of Physiology, Development & Neuroscience, University of Cambridge,

Cambridge, CB2 3EG, UK

2The Department of Physiology, University of Auckland, Auckland, New Zealand

Journal: Journal of Physiology

Submission: Editorial

Correspondence: Professor Dino A Giussani, Ph.D.

Department of Physiology Development & Neuroscience

Downing Street

University of Cambridge

Cambridge

CB2 3EG

UK

Tel: +44 1223 333894

E-mail: dag26@cam.ac.uk

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During the history of the Earth there have been dramatic changes in its oxygen 1

(O2) availability (Graham et al. 1995). Geochemical models suggest that in the 2

mid-to-late Devonian era (ca. 380 million years ago, mya), O2 levels in the Earth’s 3

atmosphere increased from ~18 to 20%. By the late Carboniferous period (286 4

mya), the Earth’s oxygenation had risen sharply to ~35%, which palaeontologists 5

refer to as ‘the oxygen pulse’. Through the following Permian and Palaeozoic eras, 6

approximately 250 mya ago, O2 concentrations fell to ~11%. Thereafter, in the last 7

200 million years, O2 levels steadily increased again, settling at the present day 8

level of ~21%. 9

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These fluctuations in O2 availability have shaped the evolution of animal life on 11

Earth and are one of the earliest challenges in physiological history. When O2 12

availability increased animals harnessed this new fuel and grew larger irrespective 13

of their phyla. Falkowski and colleagues (2005) suggest that the doubling in O2 14

over the last 200 million years coincided with the evolution of physiological traits 15

that allowed mammals to thrive. These traits include endothermy and the 16

appearance of placentation (80-60 mya), which channelled O2 to the growing 17

conceptus, thereby allowing mammalian diversification. Since the Earth became 18

better oxygenated, the greatest challenge to aerobic animals became hypoxia. 19

Therefore, animals evolved compensatory mechanisms to withstand episodes of O2 20

deprivation. How organisms consumed, distributed and utilised O2 under normoxic 21

and hypoxic conditions became a key focus of Sir Joseph Barcroft’s research. 22

Generations of physiologists have since delineated the mechanisms which allow 23

fetal and adult animals to compensate for a low PaO2. These concepts resonate 24

through many of the papers presented in this issue of The Journal of Physiology, 25

which is devoted to celebrating the centenary of Barcroft’s research and is 26

appropriately entitled: Hypoxia, Fetal and Neonatal Physiology: 100 years on from 27

3

Sir Joseph Barcroft. The initial motivation for this volume was the centenary 1

celebration of the 1914 opening of the Physiological Laboratory, a purpose built 2

research building for the Department of Physiology on the Downing site of the 3

University of Cambridge, where Joseph Barcroft worked for most of his career. 4

5

Barcroft’s childhood and undergraduate studies 6

Joseph Barcroft, born July 26th 1872, was the second of five children of the linen 7

merchant Henry and his wife Anna. As a child in Northern Ireland, Joseph enjoyed 8

the outdoors, sports and painting, but had no formal lessons in reading, writing or 9

arithmetic until the age of seven (Plate 1). He came to Cambridge for his schooling 10

as a teenager and, whilst still at the Leys school, achieved the impressive feat of 11

obtaining a Bachelor of Science degree from the University of London (Plate 1). 12

Joseph went on to study Natural Sciences at the University of Cambridge, being 13

admitted to King’s College, where he remained as a Fellow for the rest of his life. 14

As an undergraduate, Barcroft was keenly interested in all branches of the 15

sciences; he even made one of the first British demonstrations of an X-ray 16

photograph to the Natural Sciences club. In his third undergraduate year, he 17

specialized in Physiology, when again he excelled, obtaining a first class degree in 18

1897. Although, reports suggest that he was self-deprecating about his successes, 19

claiming that he had obtained his high marks only by playing off the internal 20

against the external examiner! (Roughton, 1949a; Roughton, 1949b; Franklin, 21

1953). 22

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Barcroft’s research and 100 years on 24

Joseph Barcroft began experimental research as soon as he graduated from 25

Cambridge in 1897 and continued until the day of his death aged 74 (Frankin, 26

1953). He had no formal mentor or supervisor but his first project was suggested 27

4

by Langley, who was then The Professor of Physiology at Cambridge. Barcroft was 1

to investigate the role of nerves in regulating the production of saliva. This 2

involved measuring the rates of O2 uptake and carbon dioxide output as well as 3

saliva production by a small secretory gland found in the lower jaw of most 4

mammals. This research showed for the first time that nerves were important in 5

stimulating saliva production, in part, by increasing O2 consumption (Barcroft, 6

1900). It also initiated Barcroft’s life-long interest in the respiratory gases and, in 7

particular, in O2 and its association with haemoglobin in the blood. 8

9

Barcroft’s research has interested scientists for decades and many accounts of his 10

works are available today. In this issue of The Journal of Physiology, there are 11

additional biographical articles. Lawrence Longo describes this Victorian 12

Physiologist's Contributions to a Half Century of Discovery with traditional authority 13

not only in the understanding of physiology but also with command as a medical 14

historian (Longo, 2015). John West (2015) writes a controversial piece highlighting 15

Barcroft's bold assertion that all dwellers at high altitudes are persons of impaired 16

physical and mental powers (Barcroft, 1925), a statement that understandably 17

continues to trigger much ongoing discussion today! Finally, Peter Nathanielsz 18

(2015) adds a personal touch, reporting on the 1972 symposium on Fetal and 19

Neonatal Physiology that he helped organise for the Physiological Society to 20

celebrate the centenary of Joseph Bancroft’s birth. Many of these biographical 21

accounts state that from about 1900, Barcroft began working on the handling of 22

gases in the blood more directly. He was interested in how tissues of the body 23

received and used O2, especially at high altitude where O2 is limited in availability. 24

In 1910 and 1911, he led mountain expeditions to Tenerife and Italy to study 25

oxygenation and haemoglobin function at lower than normal partial pressures of 26

O2. This period of research culminated in the publication of his first book, The 27

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Respiratory Functions of Blood in 1914. His expertise in this area, and his success 1

as a scientist generally, were based on two main attributes; first, his technical 2

ability in making new equipment to measure, for instance, the volume and partial 3

pressures of gases in small amounts of blood and, secondly, his intellectual ability 4

in designing and performing experiments that others thought impossible, often 5

carrying them out on himself (Plate 2). An early film on the study of the blood-6

oxygen equilibrium, originally made by Joseph Barcroft and found by chance in 7

some obscure corner of Cambridge beautifully, and somewhat amusingly, 8

demonstrate these attributes (https://archive.org/details/Bloodandrespiration-9

wellcome, Wellcome Trust). 10

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As a Quaker, Barcroft was seconded to government research at Porton Down during 12

the First World War as the Chief Physiologist. Given his interest in respiration, his 13

instructions were to investigate the causes, consequences and possible treatments 14

of gas poisoning, a common weapon in trench warfare on the Western front. Again, 15

his investigations were frequently ‘self-experiments’, pushing himself to the limits 16

of his own physiological compensation on several occasions (Roughton, 1949a; 17

Roughton, 1949b; Franklin, 1953). After the war, Barcroft returned to Cambridge 18

and undertook more basic research on the distribution of blood to different organs 19

and on the question of whether O2 was secreted actively into blood from the lungs 20

when its atmospheric concentration was low. To answer this question, Barcroft 21

took two different approaches. First, he led another, longer expedition to Cerro de 22

Pasco in Peru from 1920-1921 to study pulmonary gas exchange and blood 23

chemistry at high altitude. This expedition was funded by the Royal Society and 24

was better equipped and manned than his previous expeditions. It involved taking 25

a train with a mobile laboratory car to an altitude of 4,328 m (Plate 3) and 26

analysing the O2 content of blood by direct arterial puncture of expedition 27

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volunteers and of members of non-native and native communities who had been 1

living at this altitude for months or several generations, respectively. An account of 2

this expedition can be read in the transcripts of letters from Barcroft sent home to 3

his family that are housed in the archives of The Royal Society in London and in the 4

library of the Department of Physiology, Development and Neuroscience at 5

Cambridge. Secondly, he built himself an air-tight glass chamber at the 6

Physiological Laboratory, where he could live and exercise at O2 levels equivalent to 7

4,877 m (Plate 3; Barcroft, 1920). In this latter paper, Barcroft adds some 8

colourful description of his self experimentation, including radial artery 9

catheterisation, and recovery following fainting with tea and brandy! Barcroft was 10

so enthusiastic about these experiments that he had to be extracted by his 11

colleagues from his hypoxic ‘room’ after close to 6 days in situ (Franklin, 1953). 12

Together, these experiments proved that O2 was not secreted from the lungs but 13

moved into the blood by diffusion, although there were changes in the O2 14

dissociation curve of blood with acclimatisation to low O2 levels. He, therefore, 15

updated his book, The Respiratory Functions of Blood and divided it into two parts, 16

one dealing with the lessons from high altitude (1925) and the other with the 17

contribution of haemoglobin to tissue O2 delivery (1928). 18

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Fascination with the physiological effects of high altitude persists to this day. In 20

this issue of The Journal of Physiology, Murray & Horcroft (2015) and Jacobs and 21

colleagues (2015) expand on the effects of high altitude on mitochondrial function 22

and density in muscle, recapitulating Barcroft’s self-experimentation and reporting 23

on investigations performed on biopsies of their own vastus lateralis! Similarly, 24

Veith et al. (2015) and Hodson et al. (2015) bring us up-to-date with the molecular 25

mechanisms underlying HIF-induced pulmonary hypertension and the importance of 26

the principal HIF prolyl hydroxylase PHD2/HIF-2α enzyme-substrate couple in 27

7

modulating ventilatory sensitivity to hypoxia. Finally, Fatemian et al. (2015) 1

report that the peripheral chemoreflex sensitivity to CO2 can serve as a predictor of 2

human acclimatization to high altitude hypoxia. 3

4

The final phase of Barcroft’s research for which he is best remembered now did not 5

begin until 1932, when he was 60 and, upon the death of John Newport Langley, he 6

was appointed to be The Professor of Physiology at Cambridge. Barcroft became 7

intrigued in how the fetus, developing within its mother, received enough O2 to 8

grow so rapidly. This was one area in which he could not experiment on himself so 9

he used pregnant animal models to determine how fetuses respire. He thought that 10

the fetus had a lower basal arterial O2 level than its mother and might be like the 11

acclimatised mountaineer at high altitude. So he set about studying how fetuses 12

survived and thrived on ‘Everest in utero’, a phrase he coined which has been used 13

extensively since to describe the conditions in which the fetus normally develops 14

(Barcroft, 1935). Using pregnant sheep, under the influence of anaesthesia, in 15

acute preparations developed by Huggett (1927) where fetuses were delivered into 16

a warm water bath, Barcroft measured placental function, fetal growth rate, fetal 17

haemoglobin and O2 carrying capacity, fetal respiratory movements, fetal and 18

placental blood flow and the changes that occur in the fetal circulation and lungs at 19

the time of birth. These studies resulted in the publication of his final book, 20

Researches on Pre-natal Life, in 1946, the year before he died. 21

22

Without question, this publication laid the foundation for Fetal and Neonatal 23

Physiology as a separate branch of Physiology and opened up a new era of basic 24

and clinical research into fetal growth and development during healthy and 25

compromised pregnancies. Although the sheep remains the animal model of choice 26

for studying pregnancy and fetal development, Barcroft’s initial acute preparation 27

8

has been refined to allow studies in the conscious state, through the efforts of 1

Donald Barron, one of Barcroft’s most influential post-doctoral fellows, and of 2

Barron’s post-doctoral researchers, Giacomo Meschia and Frederick Battaglia. They 3

developed the chronically catheterised fetal sheep preparation, now used 4

worldwide, which allows the study of the physiology of the mother and fetus after 5

full recovery from surgery without the confounding effects of pre-operative fasting, 6

anaesthesia and surgical stress (Meschia et al. 1965). 7

8

In this issue of the Journal of Physiology, seven papers from laboratories in North 9

and South America, Europe, Australia and New Zealand, report on findings using 10

this type of chronically-instrumented ovine preparation (Allison et al. 2015; Chang 11

et al. 2015; Clifton et al. 2015; Galinsky et al. 2015; Giussani, 2015; Herrera et al. 12

2015; Lear et al. 2015). Giussani (2015) reviews the fetal cardiovascular defence 13

to acute hypoxia, highlighting neural, endocrine and vascular redox mechanisms, 14

and introducing the concept of the fetal brain sparing index. Herrera et al. (2015) 15

report on cardiovascular function in term fetal sheep conceived, gestated and 16

studied under the influence of chronic hypoxia by exploiting the natural laboratory 17

of the high altitude of the Andean altiplano. Almost ‘keeping it in the family’, again 18

recapitulating many of Barcroft’s preoccupations, Allison et al. (2015) bring the 19

Andean mountains back to Cambridge. Combining bespoke isobaric hypoxic 20

chambers and a wireless data acquisition system, they introduce a new technique 21

that is able to maintain chronically instrumented pregnant ewes and their fetuses 22

under isobaric chronic hypoxia for most of gestation at lower levels than can be 23

achieved by habitable high altitude and of direct relevance to the degree of hypoxia 24

seen in human infants with significant intrauterine growth restriction. The 25

technology also permits, for the first time, longitudinal wireless recording of 26

maternal and fetal cardiovascular function in free-moving animals, including beat-27

9

to-beat alterations in arterial blood pressure and blood flow signals in regional 1

circulations. Lear and colleagues (2015) challenge the long held assumption that 2

the sympathetic nervous system mediates fetal heart rate (FHR) variability in 3

labour. The clinical significance of this report is important and is reviewed by Shaw 4

et al. (2015), as this finding directly contradicts the established clinical 5

interpretation that preserved FHR variability implies adequate fetal physiological 6

compensation. Galinsky et al. (2015) caution on the clinical use of magnesium 7

sulphate for the treatment for pre-eclampsia and perinatal neuroprotection, as it 8

alters the perfusion of several vascular beds during acute asphyxia; effects which 9

may place the preterm fetus at greater risk of intestinal and renal compromise. 10

Chang et al. (2015) use a transcriptomics approach to predict that hypoxia 11

activates inflammatory pathways and reduces metabolism in the fetal kidney 12

cortex, and show that ketamine ameliorates this response. Thus, their data suggest 13

that ketamine may have therapeutic potential for protection from ischaemic renal 14

damage. Clifton et al. (2015) introduce an ovine experimental model to investigate 15

the effects on the fetus of maternal asthma in pregnancy, permitting evaluation of 16

current as well as novel clinical interventions. 17

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This issue of the Journal of Physiology also focuses on continuing studies on the 19

placenta, the interface between mother and the fetus. In placentae obtained from 20

normotensive and pre-eclamptic women at sea level and at high altitude, Kurlak et 21

al. (2015) report that the placental renin-angiotensin-system is responsive to 22

changes in tissue oxygenation. They introduce the concept that this could be 23

important in the interplay between reactive oxygen species as cell-signalling 24

molecules for angiogenesis and, hence, placental development and function. Three 25

studies that model hypoxic pregnancy in mice highlight placental adaptations to 26

decreased oxygenation at functional, cellular and molecular levels. Higgins et al. 27

10

(2015) report that hypoxia modifies the placental transport phenotype and resource 1

allocation to fetal growth. The study highlights that there appears to be a threshold 2

between 13% and 10% of maternal inspired O2, corresponding to altitudes between 3

ca. 3700m and 5800m, at which the mouse placenta can no longer adapt to 4

support fetal resource allocation with implications for human pregnancies at higher 5

altitudes. Using the same mouse model of hypoxic pregnancy, Skeffington and 6

colleagues report that adenosine monophosphate-activated protein kinase (AMPK) 7

is a uterine artery vasodilator and may provide a key molecular link between 8

maternal uterine vascular responses, placental function and fetal growth in normal 9

and complicated pregnancy. They show that manipulation of AMPK may be a novel 10

mechanism for developing new therapies in pregnancies complicated by chronic 11

hypoxia. Finally, Matheson et al. (2015) report further placental adaptations to 12

chronic hypoxia at the molecular level, showing activation of endoplasmic reticulum 13

stress, a conserved homeostatic response that mediates translational arrest 14

through phosphorylation of the eukaryotic initiation factor 2 subunit alpha (eIF2α), 15

which may underlie fetal growth restriction. They also report sexually dimorphic 16

morphological and molecular changes in the murine placenta exposed to 17

normobaric hypoxia throughout pregnancy. 18

19

Further reports in this issue of the Journal of Physiology focus on the transition to 20

postnatal life and potential therapy to ameliorate the problems that face the 21

vulnerable infant. In a beautiful imaging study using simultaneous phase-contrast 22

X-ray and angiography in rabbits, Lang et al. (2015) discuss previously unknown 23

mechanisms responsible for mediating the increase in pulmonary blood flow at 24

birth. They conclude that mechanisms unrelated to oxygenation or to the spatial 25

relationships that match ventilation to perfusion, initiate the large increase in 26

pulmonary blood flow at birth. McGillick et al. (2015) provide evidence for 27

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stimulatory effects of vascular endothelial growth factor (VEGF) administration on 1

structural maturation in the lung of both the normally grown and placentally-2

restricted IUGR sheep fetus, raising VEGF as an interesting potential candidate for 3

therapy against respiratory distress syndrome of the preterm infant. Additional 4

candidate protective therapy for newborn life is provided by Aridas and colleagues 5

(2015), who report that umbilical cord blood stem cells administered after perinatal 6

asphyxia can convey neuro-protection in newborn lambs, with translational 7

potential for the treatment of human infants following hypoxic ischaemic 8

encephalopathy. In contrast, Barton et al. (2015) caution on the potential adverse 9

side effects of erythropoietin administration as a neuroprotective therapy. They 10

report that erythropoietin administration within minutes of the onset of injurious 11

ventilation in newborn lambs can amplify pro-inflammatory cytokine gene 12

expression in both the periventricular and subcortical white matter. 13

14

In 1946, Barcroft wrote: “never losing sight of the fact that one day the call will 15

come and the fetus will be born. Not only has the fetus to develop a fundamental 16

life which will suffice for intrauterine conditions, but at the same time it has to 17

develop an economy which will understand the shock of birth, and will suffice, nay 18

more than suffice, for its new environment.” This statement hints that Barcroft 19

begun to think like many developmental physiologists do today, agreeing that 20

sometimes compensation carries a price. Now we know that compensatory or 21

adaptive responses to adverse intrauterine conditions, while beneficial in terms of 22

survival in utero, may sometimes trigger unwanted adverse side effects in the 23

offspring, increasing the risk of pathology in later life (Barker, 1998; Fowden et al. 24

2006; Gluckman et al. 2008). In fact, programmed cardiovascular and metabolic 25

disease in later life specifically linked to chronic fetal hypoxia has been recently 26

reviewed by Giussani & Davidge (2013). While chronic fetal hypoxia is known to 27

12

increase the risk of cardiac and endothelial dysfunction in later life (Giussani et al. 1

2012), recent focus has been on the effects of combined pre-and post-natal 2

challenges. In this issue of the Journal of Physiology, Walton et al. (2015) show 3

that late gestational hypoxia combined with a postnatal high-salt diet exacerbates 4

the programming of endothelial dysfunction and arterial stiffness in adult mouse 5

offspring. Shah and colleagues (2015) report that resveratrol, a natural polyphenol 6

found in grape skin, improves cardiovascular and metabolic health in adult rat 7

offspring exposed to prenatal hypoxia and a postnatal high-fat diet, and that this 8

protective effect is independent of the sex of the offspring. Vega at al. (2015) 9

conclude that resveratrol also partially prevents increased indices of oxidative 10

stress in the mother, placenta and offspring in pregnancy complicated by maternal 11

under-nutrition and that some of these effects protect the mother and offspring 12

against metabolic dysfunction. 13

Barcroft: the person, his final days and his legacy 14

Joseph Barcroft became much loved for his enthusiasm, kindness and attention to 15

detail as a mentor and teacher as well as being a great communicator, often 16

lecturing without notes (Plate 4). In the decade preceding World War I, he had 17

supervised almost every Cambridge physiologist, many of whom became successful 18

scientists themselves. According to his biographer, Francis Roughton (1949a): “one 19

of his most charming characteristics was that he always took particular trouble to 20

get to know and to help those working on all rungs of the ladder, from top to 21

bottom, of any institution or concern with which he was connected”. During his 22

career, Barcroft published >300 papers, books and research reports, and travelled 23

widely within the UK and abroad to scientific and other educational meetings. He 24

talked “in that simple, always exciting and slightly breathless way he had, making 25

all he had discovered seem so self-evident, poking fun at himself and paying 26

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generous tribute to his collaborators” (Roughton, 1949a, Roughton, 1949b). 1

Barcroft also had an ability to attract bright young people to work with him, many 2

of whom continued with research into hypoxia, and fetal and neonatal physiology 3

after his death. It was common knowledge that Barcroft attributed his success to 4

only one thing - a daily afternoon nap! Although Joseph Barcroft retired as 5

Professor in 1937, he remained scientifically active until his sudden death of a heart 6

attack ten years later. According to his colleague Roughton, that morning, Barcroft 7

had been his usual energetic, shrewd and good-humoured self, departing to catch a 8

bus with a quip and a smile. When they later heard the news of his death, his 9

colleagues remarked that Joseph Barcroft had gone on doing first class work right 10

up to the last moment of his life, and for him ‘physiology was the greatest sport in 11

the world’! (Plate 5). This special issue of The Journal of Physiology is a testament 12

to Barcroft’s continuing legacy and to the fascination many of us still find in the 13

unanswered physiological questions that drove his research more than 100 years 14

ago. 15

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Allison BJ, Brain KL, Niu Y, Kane AD, Herrera EA, Thakor AS, Botting KJ, Cross CM, 2 Itani N, Skeffington KL, Beck C, Giussani DA (2015). Fetal in vivo continuous 3 cardiovascular function during chronic hypoxia. J Physiol. In Press. 4 5 Aridas JD, McDonald, Paton MC, Yawno T, Sutherland AE, Nitsos I, Pham Y, 6 Ditchfield M, Fahey MC, Wong F, Malhotra A, Castillo-Melendez M, Bhakoo K, 7 Wallace EM, Jenkin G, Miller SL (2015). Cord blood mononuclear cells prevent 8 neuronal apoptosis in response to perinatal asphyxia in the newborn lamb. J 9 Physiol. In Press. 10 11 Barcroft J (1900). The gaseous metabolism of the submaxillary gland: Part I. On 12 methods, with a description of an apparatus for gas analysis. J Physiol. 25(4), 13 265-82. 14 15 Barcroft J (1914). The Respiratory Function of the Blood. Cambridge University 16 Press, Cambridge. 17 18 Barcroft J, Cooke A, Hartridge H, Parsons TR, Parsons W (1920). The flow of 19 oxygen through the pulmonary epithelium. J Physiol. 18;53(6):450-72. 20 21 Barcroft J (1925). The Respiratory Function of the Blood, Part I: Lessons from High 22 Altitudes. Cambridge University Press, Cambridge, UK. 23 24 Barcroft J (1928). The Respiratory Function of the Blood, Part II: Haemoglobin, 2nd 25 edn. Cambridge University Press, Cambridge, UK. 26 27 Barcroft J (1935). The Croonian lecture: foetal respiration. Proc R Soc Lond B 118, 28 242-263. 29 30 Barcroft J (1946). Researches on Pre-natal Life, Vol. I. Blackwell Scientific 31 Publications, Oxford. 32 33 Barker DJP (1998). Mothers, Babies, and Disease in Later Life (Churchill 34 Livingstone, Edinburgh, UK). 35 36 Barton SK, McDougall AR, Melville JM, Moss TJ, Zahra VA, Lim T, Crossley KJ, 37 Polglase GR, Tolcos M. (2015). Differential short-term regional effects of early high 38 dose erythropoietin on white matter in preterm lambs after mechanical ventilation. 39 J Physiol. In Press. 40 41 Chang EI, Zárate MA, Rabaglino MB, Richards ER, Keller-Wood M, Wood CE (2015). 42 Ketamine suppresses hypoxia-induced inflammatory responses in the late gestation 43 ovine fetal kidney cortex. J Physiol. In Press. 44 45 Clifton VL, Moss TJ, Wooldridge AL, Gatford KL, Liravi B, Kim D, Muhlhausler BS, 46 Morrison JL, Davies A, De Matteo R, Wallace MJ, Bischof RJ (2015). Development of 47 an experimental model of maternal allergic asthma during 48 pregnancy. J Physiol. In Press. 49 50

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18

LEGENDS

Plate 1. Joseph Barcroft, a month before his third birthday (left) and as Bachelor of

Science of the University of London (19 years of age, right).

Plate 2. Joseph Barcroft’s apparatus for blood gas extraction (1900). Franklin

1953.

Plate 3. Joseph Barcroft inside the ‘Glass chamber’ during his experiment in 1920.

Franklin 1953.

Plate 4. Joseph Barcroft lecturing in Lecture Theatre 1 at the Physiological

Laboratory, University of Cambridge in 1935 (left) and discussing science with

August Krogh in 1929 (right).

Plate 5. Joseph Barcroft driving off (1929, left) and in the preface to his book “The

Respiratory Function of the Blood”, 1914, right in which he stated: ‘At one time,

which seems too long ago, most of my leisure was spent in boats. In them I

learned what little I know of research, not of technique or of physiology, but of the

qualities essential to those who would venture beyond the visible horizon.‘

19

ACKNOWLEDEGEMENTS

Dino Giussani is supported by the British Heart Foundation, The Biotechnology and

Biological Sciences Research Council, The Royal Society, The Wellcome Trust,

Action Medical Research and the Isaac Newton Trust.

CONFLICTS OF INTEREST DISCLOSURES

The authors declare no conflicts of interest.

Plate 1. Joseph Barcroft, a month before his third birthday (left) and as Bachelor of Science of the University of London (19 years of age, right). Franklin 1953.

Plate 2. Joseph Barcroft’s apparatus for blood gas extraction (1900). Franklin 1953.

Plate 3. Joseph Barcroft inside the ‘Glass chamber’ during his experiment in 1920. Franklin 1953.

Plate 4. Joseph Barcroft lecturing wearing a gown in Lecture Theatre 1 at the Physiological Laboratory, University of Cambridge in 1935 (left) and discussing science with August Krogh in 1929 (right). Franklin 1953.

Plate 5. Joseph Barcroft driving off (1929, left) and in the preface to his book “The Respiratory Function of the Blood”, 1914 (right) in which he stated: ‘At one time, which seems too long ago, most of my leisure was spent in boats. In them I learned what little I know of research, not of technique or of physiology, but of the qualities essential to those who would venture beyond the visible horizon.‘ Franklin 1953.