NUTRITION AND THE CHANGES IN THE TISSUES. 373 



foods are combined under the influences of the living cell 

 with the nitrogenous remnant there of a previous disintegra- 

 tion, and so built up into living tissue. These sugars and 

 fats supply that part of the food which in the disintegration 

 of the living tissue is lost ; they supply the carbon and the 

 hydrogen. As these, therefore, cannot be used a second 

 time, new amounts of sugars or fats must be taken to replace 

 them. In this way the consumption of sugars and fats of 

 the blood must be proportional to the amount of work done. 

 Of course, if sugars and fats are not given in sufficient 

 amounts, or are excluded altogether, the body is able to 

 derive this oxygen, carbon and hydrogen from proteids 

 alone. But then this great excess of proteid must be first 

 dissociated in the liver, and so sugar or fat produced, and 

 these be the immediate foods of the tissues. Carnivorous 

 animals can live upon a diet of meat alone, and in such cases 

 the quantity of meat will, to a large extent, be proportional 

 to the work done. But the proportion is not in the nitrogen 

 which it contains, but in the carbon and hydrogen which 

 are needed. 



An ideal physiological diet, therefore, is one that con- 

 tains enough proteid to replace the wear and tear of the 

 body on a high nutritive equilibrium, and then has the car- 

 bohydrates and fats as the sources from which the carbon 

 and hydrogen are derived. Increased work, therefore, would 

 demand not primarily an increase in the proteids, but would 

 at once demand a proportional increase in the fats and 

 sugars. 



It was pointed out that a little of the nitrogenous rem- 

 nant which results from the disintegration of a part of the 

 living cell is lost, possibly accidentally, more probably be- 

 cause it is no longer fit to be used. This nitrogenous rem- 

 nant no longer retained by the cell is dropped into the blood 

 and is by the blood carried to the liver. This substance 

 appears in several different stages of oxidation and is known 

 to the chemist as kreatin or kreatinin. This kreatin aris- 

 ing in the tissues of the body and carried to the liver by the 



