440 NUTRITION ANIMAL HEAT AND FORCE. 



promptly disappears as sugar, usually in the passage of the blood through 

 the lungs. In addition to the glycogen formed from the carbohydrates of 

 food, the liver is capable of forming glycogen from other substances, as 'is 

 shown by the presence of glycogen in the liver of carnivorous animals. It is 

 probable that the glycogen thus produced is formed from albuminoid matters 

 and not from fats. The exact mechanism of the destruction of carbohydrates 

 in the organism has not been fully understood, although it is admitted that 

 these substances are important factors in the production of animal heat. The 

 presence of alcohol in very small quantity in the normal blood has been 

 demonstrated by Ford (1872). If this be admitted and the accuracy of the 

 observations by Ford seems to have been absolute it is reasonable to sup- 

 pose that the small quantity of sugar constantly discharged into the blood by 

 the liver is converted into alcohol, which is promptly oxidized, being con- 

 verted into carbon dioxide and water. The carbohydrates, in contributing to 

 calorification, are very important in saving destruction of the albuminoid 

 constituents of the body. In this process the carbohydrates and the fats act 

 together and in the same way ; and in this action they are capable of mutu- 

 ally replacing each other. 



The fats taken as food are either consumed in the organism or are de- 

 posited in the form of adipose tissue. That the fats are consumed, there can 

 be no doubt ; for in the normal alimentation of man, fat is a constant article, 

 and it is never discharged from the body. For a time, during absorption, 

 fat may exist in certain quantity in the blood ; but it soon disappears and is 

 either destroyed directly in the circulatory system or is deposited in the form 

 of adipose tissue to supply a certain quantity of this substance consumed. 

 That it may be destroyed directly, is proved by the consumption of fat in 

 instances where the quantity of adipose matter is insignificant; and that the 

 adipose tissue of the organism may be consumed, is shown by its rapid dis- 

 appearance in starvation. 



Formation and Deposition of Fat. The question of the formation of fat 

 in the economy is one of great importance. Whatever the exact nature of 

 the changes accompanying the destruction of non-nitrogenized matters may 

 be, it is certain that the fat stored up in the body is consumed, when there 

 is a deficiency in any of the constituents of food, as well as that which is 

 taken into the alimentary canal. It is rendered probable, indeed, by the few 

 experiments that have been made upon the subject, that obesity increases the 

 power of resistance to inanition. At all events, in starvation, the fatty con- 

 stituents of the body are the first to be consumed, and they almost entirely 

 disappear before death. Sugar is never deposited in any part of the organ- 

 ism, and it is merely a temporary constituent of the blood. If the sugars 

 and fats have, in certain regards, similar relations to nutrition, and if, in addi- 

 tion to the mechanical uses of fat, it may be retained in the organism for use 

 under extraordinary conditions, it becomes important to ascertain the mech- 

 anism of its production and deposition. 



The production of fatty matter by certain insects, in excess of the fat 

 supplied with the food, was established long ago by the researches of Huber ; 



