CONSUMPTION OF OXYGEN. 139 



quite small; and the observations of Legallois, on rabbits, made every five 

 days during the first month of life, show a rapidly increasing demand for 

 oxygen. 



The consumption of oxygen is greater in lean than in very fat animals, 

 provided they be in perfect health. The consumption is greater, also, in car- 

 nivorous than in herbivorous animals ; and in animals of different sizes, it is 

 relatively much greater in those which are very small. In small birds, such 

 as the sparrow, the relative quantity of oxygen absorbed was ten times greater 

 than in the fowl (Regnault and Reiset). 



During sleep the quantity of oxygen consumed is considerably dimin- 

 ished ; and in hibernation it is so small, that Spallanzani could not detect 

 any difference in the composition of the air in which a marmot, in a state of 

 torpor, had remained for three hours. In experiments on a marmot in hiber- 

 nation, Regnault and Reiset observed a reduction in the oxygen consumed to 

 about ^g- of the ordinary quantity. 



It has been shown by experiments, that the consumption of oxygen bears 

 a nearly constant ratio to the production of carbon dioxide ; and as the 

 observations upon the influence of sex, the number of respiratory acts etc., on 

 the activity of the respiratory processes have been made chiefly with reference 

 to the carbon dioxide exhaled, these influences will be considered in connec- 

 tion with the products of respiration. 



Experiments on the effect of increasing the proportion of oxygen in the 

 air have led to varied results in the hands of different observers. Regnault 

 and Reiset, whose observations on this point are generally accepted, did not 

 discover any increase in the consumption of oxygen when this gas was largely 

 in excess in the atmosphere. 



The results of confining an animal in an atmosphere composed of twenty- 

 one parts of oxygen and seventy-nine parts of hydrogen are very remarkable. 

 When hydrogen is thus substituted for the nitrogen of the air, the consump- 

 tion of oxygen is largely increased. Regnault and Reiset attributed this to 

 the superior refrigerating power of the hydrogen ; but a more rational expla- 

 nation would seem to be in its greater diffusibility. Hydrogen is the most 

 diffusible of ail gases ; and when introduced into the lungs in place of the 

 nitrogen of the air, the vitiated air, charged with carbon dioxide, is undoubt- 

 edly more readily removed from the deep portions of the lungs, giving place 

 to the mixture of hydrogen and oxygen. It is probably for this reason that 

 the quantity of oxygen consumed is increased. It is probable that the nitro- 

 gen of the air plays an important part in the phenomena of respiration, by 

 virtue of its degree of diffusibility. 



In view of the great variations in the consumption of oxygen, dependent 

 on different physiological conditions, such as digestion, exercise, temperature 

 etc., it is impossible to fix upon any number which will represent, even ap- 

 proximately, the average quantity consumed per hour. The estimate arrived 

 at by Longet, from a comparison of the results obtained by different reliable 

 observers, is perhaps as near the truth as possible. This estimate puts the 

 hourly consumption at 1,220 to 1,525 cubic inches (20 to 25 litres), " in an 



