45 



sufflation is not used. The duration of life was 7, 12, 13 

 and 17 days in four insufflated tortoises. When death occurred 

 in these four animals, they had been left without insufflation 

 more than five or six hours, and very likely they would have 

 lived longer had they been insufflated more frequently. In 

 four non-insufflated tortoises life lasted 3, 7, 19 and 23 hours. 

 These comparative experiments were made in summer in a tem- 

 perature varying from 64 to 86 F. (18 to 30 Cs.) The in- 

 sufflated tortoises lived longer in summer than non-insufflated 

 tortoises in winter. 



From all these facts it is evident that in animals deprived of 

 the medulla oblongata, death is principally caused by insuffi- 

 ciency of respiration. 



XVII ON THE INFLUENCE OF THE TEMPERATURE OF A WARM- 

 BLOODED ANIMAL UPON THE DURATION OF ITS LIFE WHEN IT 

 IS ASPHYXIATED. 



One of the most positive facts in physiology is that every 

 animal needs oxygen in order to live. But if there is a com- 

 plete uniformity as to the necessity of oxygen for all animals, 

 there is also the greatest variety between the different species as 

 to the quantity of that gas which is necessary for the mainte- 

 ance of life. Very probably a great part of the physiological 

 differences between different animals, comes from the difference 

 in the quantity of oxygen absorbed by their blood in a given 

 time. The most important cause of the differences existing be- 

 tween cold and warm-blooded animals, and between young and 

 adult animals, is to be found in the differences in the quantity 

 of oxygen they absorb. 



It is very remarkable that one of the principal laws relative 

 to the anatomical differences existing between the different spe- 

 cies of animals, appears to be also a law regulating their phy- 

 siological differences. In an anatomical point of view, a mam- 

 mal, at the different periods of its development, presents 

 alternately the forms of many different beings. In a physiolo- 

 gical point of view, a corresponding transformation occurs for 

 the mammals. They exhibit alternately the same phenomena 

 of life exhibited by many other different animals. For instance, 

 before its birth, the mode of breathing of a mammal is the 



