3 88 PHYSIOLOGICAL CHEMISTRY. 



of fat the latter must amount to about 104 gm. This repre- 

 sents the true gain in body weight; the weighings showed a 

 gain of only 50 gm. The discrepancy may be accounted for 

 by assuming an excessive excretion of urine. No such dis- 

 crepancy would appear if the urine were passed from the blad- 

 der as fast as formed, but as it is collected at intervals it is 

 not possible to obtain exactly comparable results. 



In the feces there must be some carbon derived from fats; 

 but the amount cannot be large, because for the nitrogen of the 

 feces we must calculate at least 10 or 12 gm. to correspond. 

 This would leave about 5 gm. of carbon from other sources, 

 accounting for the discrepancy between consumed fat and 

 deposited fat. 



The above calculations illustrate the principles involved ; in an actual 

 practical observation the method would be the same, but the interpretation 

 of results might not be as simple, especially with a low respiratory quotient 

 found. In the above tables the salts taken with the food are assumed to 

 include those to be formed by the oxidation of the protein, and the latter 

 substance figured as income is assumed to consist of the organic elements 

 only. A slight error is introduced in the calculation in this way, but that 

 is not considered. In actual practice, of the carbohydrates some little 

 would escape complete metabolism. The above results would correspond 

 to a completely burned carbohydrate. 



In the above table of observations the total oxygen in the consumed 

 substances, including the water, is 2,044 g m - In the excreted products, 

 allowing 30 gm. for the solids of the urine and feces coming from bodies 

 other than the original salts, the oxygen appears to amount to about 2,800 

 gm. The difference shows an excess of 756 gm. while the calculation 

 above gave 708 gm. of oxygen taken in. The discrepancy is due to the 

 excess of water excreted as urine. It will be noticed also that there is 

 a great excess of excreted water over the 2,000 gm. consumed. This 

 amounts to over 350 gm., of which 300 gm. would come from the com- 

 bustion of the carbohydrates and proteins metabolized. 



SKIN RESPIRATION. 



It is usually assumed that the gaseous exchange is wholly 

 through the lungs, but this is not quite correct. Experiments 

 with men and animals have shown an absorption of oxygen 

 and an escape of carbon dioxide through the skin. A num- 

 ber of observers have put results for the latter on record which. 



