332 LECTURE XV. 



kinds of food, for the diabetic can perform muscular work, even though 

 he is not able, in proportion to the severity of the disease, to utilize to 

 advantage the most important source of energy, the carbohydrates. For 

 him the carbohydrates scarcely come into consideration as a source of 

 energy. Evidently the diabetic performs his work at the expense of other 

 food material. We cannot look upon this proof as entirely convincing, 

 for it is precisely those observations dealing with diabetics which have led 

 to the assumption, that sugar is produced from the two other organic 

 nutrients: albumin and fat. Why does the diabetic patient produce 

 sugar from these? Why does he not utilize these according to their 

 calorific value? Why does he carry out the extremely complicated 

 chemical changes, some of which are so difficult to understand? Cer- 

 tainly not in order to eliminate more sugar. These transformations must 

 have a deeper significance. Is this a normal process which comes to light 

 because of an insufficient utilization of the products formed, or are we to 

 look upon the production of sugar from fat and albumin as a derangement 

 of the entire metabolism? These are enigmas, the solution of which still 

 reaches into the far-distant future. At all events, we repeat once again, 

 nowhere else does the question appear as vital as here, as to whether 

 specific atomic groupings are not normally utilized for definite purposes. 

 Nothing is of greater promise in the entire field of biological investigation 

 than the clearing up of just such uncertainties and contradictions. Such 

 work must lead to new problems and new results. We have, on the one 

 hand, the claim that large amounts of sugar arise from fats and proteins, 

 while, on the other hand, there are numerous exact statements which make 

 it seem improbable that such conversions are, as a rule, necessary in normal 

 metabolism for the accomplishment of definite work. 



If we, for the moment, leave out of consideration the significance of the 

 organic nutrients as building material for the worn-out or new cells, we 

 find that their most important function is that of a source of energy. 

 Chemical energy is transmitted to the animal organism by means of 

 the food. Mechanical work is performed by the transformation of this 

 energy. Only a part of the energy is utilized in this way. Another part, 

 and in fact a very considerable one, is changed into heat. The animal 

 cell can utilize these sources of energy in two ways: first, by cleavage, 

 and second, by oxidation. Only a portion of the energy can be trans- 

 formed into kinetic energy by the former method; oxidation alone 

 furnishing the possibility for a complete utilization of the energy. Now 

 the different organic food-stuffs (carbohydrates, fats, and albumins) possess 

 different amounts of energy; i.e., they have different fuel values. The 

 amount of energy possessed by the various food materials can be deter- 

 mined by the quantity of heat which they liberate when undergoing 

 combustion. This is generally expressed in calories, a small calorie (cal.) 



