544 MISCELLANEOUS FARM SUBJECTS 



intestines on the various foods, breaking them up into other com- 

 pounds to be absorbed and used by the various parts of the body, and 

 the further changes that they undergo in the different organs of the 

 body as the liver and kidneys. Examples of physical changes are 

 the transformation of the latent heat of fats and foods into body 

 heat or into muscular work or energy. 



The ultimate purpose of the research to which such experi- 

 ments belong is the study of some of the fundamental laws of nutri- 

 tion. The plan of the present inquiry is based upon the principle 

 that the chemical and physical changes which take place within the 

 body occur in obedience to the laws of the conservation of matter 

 and energy. That the law of the conservation of matter applies 

 within the living organism no one would question. It might seem 

 equally certain that the metabolism of energy within the body takes 

 place in accordance with the law of the conservation of energy. 

 The quantitative demonstration is, however, desirable, and an at- 

 tested method for such demonstration is of fundamental importance 

 for the study of the general laws of metabolism of both matter and 

 energy. 



Since, furthermore, the main use of food is to supply material 

 and energy for nourishment, this inquiry has to do with the values 

 and uses of foods. Taken all together, therefore, we may say that 

 while the more scientific object of the research is a study of the laws 

 of nutrition, in so far as they are laws of metabolism of matter and 

 energy, the practical purpose is to learn more about how the body is 

 nourished and what are the uses and values of food. 



Apparatus. For this study expensive and complicated appa- 

 ratus is necessary and the time used is proportionately great. In- 

 vestigations have been made in many ways but those of most im- 

 portance have been by means of the respiration apparatus and the 

 respiration calorimeter. 



Various forms of respiration apparatus have been devised 

 within the last fifty years. They consist of metal-walled chambers 

 large enough for the subject (sometimes a man, sometimes a dog, 

 sheep, or other animal) to live in comfortably for several days, and 

 are furnished with devices for pumping air through and measuring 

 and analyzing it as it enters and leaves the chamber. With such 

 an apparatus it is possible not only to measure all the food and ex- 

 creta, but also the materials given off from the lungs in the breath, 

 and to make accurate determinations of the matter entering and 

 leaving the body. 



A still more elaborate apparatus, by which not only all the 

 matter passing in and out of the body may be measured, but also 

 all the heat given off from it, is called a respiration calorimeter. It 

 is like the respiration apparatus, except that it is furnished with de- 

 vices for measuring temperatures. Its main feature is a copper 

 walled chamber in which the subject of the experiment a man 

 lives, eats, drinks, sleeps, and works during a period of several days 

 and nights. This is fitted with devices for maintaining and measur- 



