LECTURE XV. 



MUTUAL RELATION BETWEEN FATS, CARBOHYDRATES, 

 AND ALBUMINS. 



II. 

 THE LAW OF ISODYNAMICS. 



So far we have considered only the most important organic nutrients 

 from one point of view, namely, their chemical composition, and sought 

 out those facts which led to the assumption that one class of substances 

 goes over into another in the animal organism. In such cases extensive 

 chemical changes take place reduction, oxidation, analysis, and synthe- 

 sis before one substance can replace another. This, however, is not 

 the only way in which one substance may appear in place of another. 

 The substitution may be a purely physical one; i.e., the energy imparted 

 to the body by the substances in question may be the most important 

 factor. In other words, we can conceive that the different organs, e.g., 

 the muscles, do not work with one single food material alone in perform- 

 ing their prescribed functions, but with representatives of all three groups 

 of nutrients. We could indeed imagine, as we have already mentioned, 1 

 that every individual cell in the body is so adjusted that it works only with 

 a definite material. We would then have to assume that the substitution 

 of one of these combustible substances by another must be preceded by a 

 transformation into the former. When we recall the facility with which 

 the vegetable organism converts carbohydrates into fats, and fats or 

 albumin, or both together into sugars, such a conception would, a priori, 

 not seem so improbable. On the other hand, in such a case the organism 

 evidently would not work economically, if it were called upon first of all 

 to produce deep-seated and far-reaching transformations, before it could 

 utilize the food materials. The entire metabolism would thus resolve 

 itself into an extremely complicated process, and such transformations 

 would make themselves felt especially in the case of a restricted diet with 

 a definite kind of food, e.g., of fats, which are deficient in oxygen, or of 

 carbohydrates, which are rich in oxygen. One might cite the diabetic as 

 proof of the fact that an organ can perform its work with the most varied 



1 Cf. Lecture XIV, p. 311. 



331 



