312 LECTURE XIV. 



carbohydrates. If the muscle cell possesses the ability of consuming 

 the fats, it hardly seems probable that it must first convert the fats 

 into carbohydrates in order to abstract the energy from them. 



If the fats were first changed into carbohydrates before they could be 

 utilized for work, then, according to Zuntz, a diet of fats exclusively would 

 require about 30 per cent more energy to perform a given amount of work 

 than would be required after a diet of carbohydrates. This, in fact, is not 

 the case. 1 



Until recently the above discussion would have been quite unnecessary. 

 The general conception was that the different food materials in the organ- 

 ism, i.e., in the tissues, and finally in the cells, were burned up directly 

 by the aid of oxygen. It was only necessary that the food material and 

 the oxygen should both be present in such form that they could react 

 together. 



The whole problem thus became a very simple one. The conviction is, 

 however, becoming more and more pronounced, that the relations are 

 much more complicated. The cells themselves participate far more 

 actively in the combustion of the food materials than we have hitherto 

 imagined. They prepare the substances for disintegration and combus- 

 tion. The fact that our foods are not attacked by the oxygen of the air, 

 has led to the assumption that the oxygen is " activated " in some manner 

 in the organism, and that this activated oxygen effects the combustion. 

 This problem of the activation of oxygen has been the main topic of 

 interest, whereas the behavior of the food materials themselves, in the 

 oxidation process, has been entirely neglected. Now it has only recently 

 been shown, as we have seen, that the diabetic possesses, as far as our 

 present knowledge is concerned, an absolutely normal capacity for oxida- 

 tion. Grape-sugar alone he consumes more or less imperfectly. As soon, 

 however, as any slight attack has been made upon the glucose molecule, 

 as soon as it becomes "opened up," the diabetic is able to consume com- 

 pletely, and to utilize, the energy contained therein. 2 We must consider 

 the possibility of a change occurring in the food by means of a cell influence 

 either directly or indirectly by means of ferments before the oxidation 

 takes place by the oxygen, which is carried to the tissues with the blood. 

 The material is first of all " opened up " so that it can be oxidized. How 

 this takes place, we do not yet know. We can imagine, however, that 

 the oxygen is first attached to the " opened " molecule, which is then 

 destroyed. We know, from the investigations of C. Harries, 3 that caout- 

 chouc, under the action of ozone, goes over into a compound rich in 



1 H. N. Heinemann: Pfliiger's Arch. 83, 44 (1901). J. Frentzel and F. Reach: 

 ibid. 83, 477 (1901). 



2 Cf. Lecture V, p. 101. 



3 C. Harries: Ber. 37, 2708 (1904); ibid. 38, 1195 (1905). 



