LECTURE XIX. 

 ANIMAL OXIDATIONS. 



IN the last lecture we attempted to trace the path of oxygen on its way 

 through the animal organism from the time of its being acquired from the 

 alveolar air to its being given up to the tissues and their cells, and, on the 

 other hand, we found that carbon dioxide is to be regarded as the end- 

 product in the action of oxygen upon the nutriment. Meanwhile, we have 

 failed to touch upon one point of greatest moment, namely, why the oxygen 

 attacks and consumes this cell-nutriment. Outside the animal organism, 

 if we expose albumin, fats, or carbohydrates to the action of oxygen at 

 the body temperature, even for a long time, there is no perceptible oxida- 

 tion of these materials. Within the animal organism, on the contrary, 

 these substances are oxidized in a short time, and the chief products of the 

 oxidation are carbon dioxide, water, and urea. Consequently, conditions 

 must prevail within the organism which facilitate the action of oxygen 

 upon the material exposed to its action. 



We are acquainted with quite a number of facts which compel us to 

 assume that, even within the animal tissues, oxygen as such is not able to 

 act upon the unchanged food. Under no circumstances should we imagine 

 for a -moment, that the oxygen supplied to the tissues, at once of its own 

 accord, begins to oxidize the different substances present in the cells. If 

 this were the case, it would be absolutely impossible for us to account for 

 quite a number of processes taking place in the animal organism. Above 

 all, it would then be unintelligible, why oxygen is brought to the cells, 

 together with the newly absorbed nourishment, without any oxidation 

 taking place until the cells are reached. The fact that the blood contains 

 the greater part of its oxygen chemically united with the hemoglobin, does 

 not suffice to explain this fact ; for it would be expected that the oxygen, 

 which was merely dissolved in the plasma, would be replaced, as soon as 

 consumed, by the oxygen in the hemoglobin. Again, it would be inex- 

 plicable why, in the combustions taking place in the cells, it is only the fuel 

 that is consumed, and not the cell-substance itself. On the other hand, we 

 have seen that the organism can lose the power of oxidizing certain sub- 

 stances, such as carbohydrates, for example, which are ordinarily consumed 

 easily, while other oxidation processes are not affected in the slightest. 

 We know now that in diabetes substances hard to oxidize are consumed 

 without difficulty; whereas, unchanged d-glucose alone has ceased to be a 



439 



