5 i4 TEXT-BOOK OF PHYSIOLOGY 



aceto-acetic acid or diacetic acid, viz.: CH 3 .CO.CH 2 .COOH, which by the 

 loss of a molecule of CO 2 yields acetone, viz.: CH 3 .CO.CH 3 . 



Acetone by a further oxidation is converted into carbon-dioxid and 

 water. Thus by these successive oxidations the stored-up energy of the 

 fat is liberated as heat. 



If fat is consumed in too large a quantity the last stage may not be 

 who lly completed and some of the acetone produced may be eliminated in 

 the urine. Analysis of the urine generally shows the presence of acetone 

 to the extent of o.oi to 0.03 grams daily. 



In diabetes these three compounds /3-oxybutyric acid, aceto-acetic acid 

 and acetone make their appearance in the urine. Since all oxidations are 

 preceded by a cleavage the inference is that in this disease there is an 

 absence of the enzyme necessary to effect the cleavage of the oxybutyric 

 acid and thus permit of further oxidation. The accumulation of this 

 acid in the body establishes the condition known as acidosis and in turn to 

 coma and death. 



The Origin of the Body Fat. i. From Protein. It is a familiar 

 observation that on the customary diet the animal body frequently accu- 

 mulates a large amount of fat. The question, therefore, has arisen as to its 

 origin, and many experiments have been made to determine it. If an animal 

 is placed oft a protein diet, fat is very seldom deposited. If the protein is 

 consumed in normal amounts, and the fats and carbohydrates in excess of 

 the normal amounts, there is generally an accumulation and storage of fat. 

 It was for a long time taught by v. Voit that the carbonaceous radical set 

 free in the metabolism of protein was retained in the body and deposited as 

 fat. This origin of fat has largely been disproven. The experimental 

 work of subsequent investigators has shown that v. Voit's results were due 

 to a faulty analysis of the food consumed ; that if certain errors are eliminated, 

 all the carbon arising from protein metabolism can be detected in the usual 

 excretions. The prevailing opinion is that fat does not arise from protein. 



The appearance of fat granules in the cells of tissues undergoing certain 

 pathologic changes was formerly regarded as evidence that the protein con- 

 stituents of these cells in their metabolism give rise to fat. This view is also 

 no longer entertained. The facts observed lead to the inference that the 

 fat thus appearing is either transported from the connective-tissue cells or is 

 deposited directly from the blood-stream; but owing to the destructive changes 

 in the cell it is no longer able to metabolize it. The fat observed in muscle - 

 and gland cells is to be regarded as an evidence of deposition rather than of 

 degeneration. 



2. From Fat. If now body fat is not a derivative of protein, the only two 

 other sources are the fats and the carbohydrates of the food. That the fat 

 of the food can be deposited is now a general belief, contrary to the former 

 belief, that the fat of the food was at once oxidized, thus sparing from oxida- 

 tion the fat arising from the protein. This belief is based on the results of 

 experiments which however are not strictly physiologic in character. Thus 

 two dogs were starved for a definite period. One was then given a large 

 amount of linseed-oil and the other large amounts of mutton fat. At the 

 end of several weeks both had accumulated fat. A post-mortem examina- 

 tion of the fat of the first dog showed that it was liquid at oC. while the 

 fat of the second dog was solid at 50 C. In another experiment a dog 



