196 The Feeding of Animals 



posited in the body, this was regarded as proof of the 

 formation of fat from protein. Such experiments as 

 these have not always been conclusive, although they 

 are regarded by some scientists as having furnished 

 proof that protein may be a source of fat. 



THE RESPIRATION APPARATUS 



After all, the investigations of the kinds described 

 fail to furnish data so accurate and so complete as are 

 necessary for entirely safe conclusions. In every in- 

 stance, one or more assumptions are involved where 

 definite proof is not furnished. Nothing short of a 

 complete record of the income and outgo of the ani- 

 mal organism during the experimental period is con- 

 clusive evidence as to whether there has been a gain 

 or loss of body substance and what is the kind and 

 extent of the growth or waste. The securing of such 

 a record is an expensive and laborious task. It re- 

 quires not only complete information in regard to the 

 quantity and composition of the food, but also an ac- 

 curate measurement of the excreta, including the feces, 

 the urine, the respiratory products and the matter 

 given off through the skin. Such measurements are 

 taken by means of a respiration apparatus, a costly 

 and complicated mechanism, a detailed description of 

 which would be of little use to most readers. It is 

 sufficient to state that this apparatus makes possible 

 the collection and analysis of all the excretory products, 

 whether solid or gaseous. The experimental man or 

 animal lives in a closed chamber into which is intro- 



