the book here translated which has become one of the great land- 

 marks of physiology — a book which stands as the very cornerstone 

 of modern altitude physiology, La pression baromctrique. Re- 

 cherches de physiologie expcrimentale , containing 1178 pages and 

 89 text figures. The first 522 pages deal with the history of altitude 

 physiology up to that date; and if Paul Bert did nothing else, we 

 should be lastingly in his debt for this masterly historical presenta- 

 tion — a model, be it said, for any student wishing to write in the 

 field of medical history. The second part, occupying 518 pages, con- 

 tains experimental protocols; the third and final part, which runs to 

 118 pages, contains his resume and conclusions, and is again a model 

 of concise, orderly and logical scientific presentation. 



What precisely did Bert prove? There had been sharp diver- 

 gence of opinion whether mountain sickness was due to diminution 

 of barometric pressure per se, or to diminution of oxygen pressure. 

 Bert performed critical experiments, keeping the absolute pressure 

 of oxygen constant while lowering the total atmospheric pressure, 

 repeating them time and again both in animals and man. By so 

 doing he proved beyond all doubt that the principal symptoms of 

 altitude sickness arise from reduced partial pressure of oxygen and 

 not from diminution of total pressure. He thus applied for the first 

 time to human respiration Dalton's concept of partial pressure 

 which has become the basis of all subsequent work in the field of 

 altitude physiology. 



In one of his vivid lectures on the history of physiology, Sir 

 Michael Foster said that science travels in circles: the concept fol- 

 lowed yesterday may be dropped today and rediscovered tomor- 

 row. One of those who did not accept Paul Bert's conclusions was 

 that picturesque physiologist of Italy, Angelo Mosso, who main- 

 tained that at altitude one breathed so deeply that carbonic acid 

 was lost with resulting alkalosis, and that oxygen-want played 

 only a small part in mountain sickness, the major symptoms be- 

 ing due to "acapnia"— loss of carbon dioxide. Few in this century, 

 save Yandell Henderson, have paid due attention to Mosso and 

 acapnia, but we are coming once again to heed what he said. More 

 is known now about acid-base relationships in blood and tissues. 

 The carotid sinus reflexes have also been discovered. When blood 

 of low oxygen saturation reaches the carotid sinus, a reflex in- 

 crease in depth and frequency of respiration occurs. The partial 

 pressure of oxygen is a primary and determining stimulus as Bert 

 maintained; but under conditions of low oxygen tension, hyper- 

 ventilation of serious proportions may occur, and we have reason 



VIII 



