SEC. 6. DIETETICS. 



We may sum up the main results of the previous sections some- 

 what in the following way. Although the body consists, like the 

 food, of proteids, fats and carbohydrates, yet the conversion of the 

 one into the other is not direct. Assimilation does not proceed in 

 such a way that the proteids of the food all become the proteids of 

 the body, the fats of the food the fats of the body, and the starch 

 and sugar of the food the glycogen, dextrin, and sugar of the body. 

 We cannot even say that the non-nitrogenous food supplies alone 

 the non-nitrogenous parts of the body, and that the nitrogenous food 

 remains as the sole source of the nitrogenous tissues. We have 

 seen that under all circumstances a certain quantity of proteid 

 food is immediately metabolized, probably while still within the 

 alimentary canal, and that an excess of proteid food may lead to 

 the accumulation of bodily fat. On the other hand, we find that 

 a large proportion of the carbonic acid of the egesta comes from 

 the metabolism taking place in nitrogenous tissues, such as 

 muscle ; and we have had proof that the energy set free by mus- 

 cular contraction may be far greater than could be supplied by the 

 proteid food taken, and that therefore the non-nitrogenous factors of 

 the metabolism which set free the energy must have ultimately come 

 from non-nitrogenous food. We have abundant evidence that the 

 various food-stuffs become more or less metabolized, and their ele- 

 ments more or less rearranged and mixed, before they appear as 

 constituents of the bodily tissues. 



