ANIMAL OXIDATIONS. 457 



of attack. We shall not enter here into a discussion of this or a number of 

 similar hypotheses. It may be merely said concerning them that they 

 are not very helpful, because we know practically nothing concerning the 

 chemistry of the protoplasm. 



Oxygen has, as we have seen, not only the function of enabling the 

 organism to make use of the energy stored up in the decomposition products 

 of the food, but it also serves frequently to prevent the cells from suffering 

 injury. It is entirely wrong to assume that oxygen, after it once enters 

 into reaction, immediately burns up the substance completely. We are 

 certain that in many cases only a partial oxidation takes place; i.e., the 

 oxidation takes place in stages. This fact also precludes any simple 

 explanation of animal or vegetable oxidations. The cell must in each 

 individual case determine the degree of oxidation. With activating of 

 the oxygen, or by the carrying of oxygen by means of a peroxide formation, 

 the course of oxidation in the animal tissues is by no means explained. 

 Exactly as the chemist may choose special oxidizing agents, and, by estab- 

 lishing the conditions, he may regulate the degree of oxidation, so in the 

 same way the cell is capable of regulating the oxidation according to its 

 requirements. Particularly instructive examples are shown by the 

 behavior of certain foreign substances, injurious to the cells, from whose 

 action the organism protects itself, as we have repeatedly seen, in a num- 

 ber of different ways. Rudolph Cohn * has shown that methylquinolin 

 is for the most part entirely oxidized, and that the same is true of 

 o-nitrobenzaldehyde. 2 With santonin, 3 Ci 5 H 18 3 , on the other hand, the 

 oxidation is not carried so far but it is changed into oxysantonin, Ci 5 Hi 8 O 4 . 

 The animal organism prepares a large number of such substances by 

 coupling them with certain substances such as sulphuric acid, glycocoll, 

 glucuronic acid, and urea. The first two of these substances just named 

 come from albumin, while glucuronic acid results from carbohydrates. 

 Sulphuric acid combines with a great many substances of a phenolic 

 nature; thus, ordinary phenol when introduced into the body leaves it in 

 the form of potassium phenyl sulphate: 4 



C 6 H 5 OH + HO . SO 3 K = C 6 H 5 . . SO 3 K + H 2 0. 



In this case, which was first noticed and is the simplest of all, the 

 coupling takes place directly. Sometimes, however, the phenol is first 

 oxidized. In this way quinol is formed, which then unites with the 

 sulphuric acid: 5 



HO . C 6 H 5 + O = HO . C 6 H 4 . OH 



HO . C 6 H 4 . OH + HO . S0 3 K = HO . C 6 H 4 . O . SO 3 K + H 2 



1 Z. physiol. Chem. 20, 210 (1895). 



2 Ibid. 17, 274 (1893). 



3 M. Jaffe: ibid. 22, 538 (1896-97). 



4 Baumann and Herter: ibid. 1, 244 (1877-78). 



5 Baumann and Preusse: Z. physiol. Chem. 3, 156 (1879). 



