86 LOCOMOTION. [CHAP. in. 



beer, &c. Liebig states, that, by the separation of a small propor- 

 tion of oxygen, any of these substances will present a composition 

 similar to that of fat, and that an equivalent of starch may be 

 changed into one of fat, by giving up one equivalent of carbonic 

 acid, and seven equivalents of oxygen. 



If, then, the system be imperfectly supplied with oxygen, while 

 organic compounds containing carbon are furnished to it in con- 

 siderable quantity, the most favourable conditions will exist for 

 the development of fat. The oxygen required will be abstracted 

 from the carbonised food, which, by that diminution of oxygen, 

 will be changed into a fat. On the other hand, exercise and 

 labour, which increase the supply of oxygen, diminish or prevent 

 the formation of fat. "The production of fat," says Liebig, "is 

 always a consequence of a deficient supply of oxygen, for oxygen 

 is absolutely indispensable for the dissipation of the excess of 

 carbon in the food. This excess of carbon, deposited in the form 

 of fat, is never seen in the Bedouin or in the Arab of the Desert, 

 who exhibits with pride to the traveller his lean, muscular, sinewy 

 limbs altogether free from fat : but in prisons and jails it appears 

 as a puffiness in the inmates, fed, as they are, on a poor and scanty 

 diet; it appears in the sedentary females of oriental countries; 

 and, finally, it is produced under the well-known conditions of the 

 fattening of domestic animals.* 



A good illustration of these views is afforded by the carnivorous 

 animals. In the wild state, living entirely on azotised food, and 

 enjoying abundance of air and exercise, they are lean; but, when 

 domesticated, living on a mixed diet, devouring a highly carbo- 

 naceous food, taking little exercise, and being imperfectly supplied 

 with oxygen, they grow fat. 



In animals that hybernate, fat is deposited in enormous quantity 

 just prior to the hybernating period, and during that time it 

 gradually disappears, supplying nutriment to the system, and 

 carbon for the respiratory process. These facts were clearly ascer- 

 tained in hedgehogs, by the celebrated Dr. Jenner. 



Liebig supposes that the formation of fat is attended with the 

 development of heat, for the oxygen disengaged in this process 

 unites with carbon derived from the same or a different source, and 

 an amount of heat is generated proportionate to the quantity of 

 carbonic acid thus formed. But it may be fairly questioned whe- 

 ther the temperature of the body is thereby elevated, since the 



* Liebig's Organic Chemistry of Physiology. 



