84 A Manual of Veterinary Physiology. 



When air is taken into the lungs it loses a certain pro- 

 portion of its oxygen and gains a considerable amount of 

 carbonic acid, and perhaps some other gases. More oxygen 

 is abstracted from it than is replaced by carbonic acid, so 

 that if both volumes be reduced to standard barometrical 

 pressure and temperature, there is actually less air returned 

 during expiration than entered by inspiration; owing, how- 

 ever, to the expansion caused by the warming it undergoes, 

 the expired air is larger in volume than the inspired. 



The proportion which the oxygen absorbed bears to the 

 carbonic acid given off is termed the respiratory quotient, 



CO 



and is expressed as -• The quotient varies with different 



animals, and probably depends upon the nature of the 



diet. 



In herbivora the respiratory quotient is "9 to 1 

 In carnivora „ ,, ,, "75 „ '8 



In omnivora „ „ „ '87 



(Mink)* 



which reads thus, for every 1 part of oxygen absorbed by 

 herbivora there is produced -9 to 1 part of carbonic acid, 

 and for every 1 part of oxygen absorbed by carnivora "75 to 

 •8 parts of C0. 2 are produced. In carnivora it will be 

 observed that the amount of C0. 2 produced is considerably 

 less than the amount of oxygen absorbed. 



We have said that there are other gases returned from 

 the lungs besides CO., and ; as very little is known about 

 these, we had better dispose of them at once. According to 

 Reiset, both hydrogen and marsh gas are given off in the 

 expired air of ruminants; in fact, he places the latter at 

 183 cubic inches in 24 hours. Both are supposed to be 

 derived from the intestinal canal, being absorbed into the 

 blood by the vessels of the intestinal wall. In my own 

 experiments on the gases of respiration, 1 found, after 

 deducting the oxygen, carbonic acid, and nitrogen, that a 

 balance remained, the nature of which was unfortunately 



* Quoted by M'Kenariok. 



