1236 PHYSIOLOGY 



substance) undergoes oxidation with, the formation of nitrite. In the 

 slow spontaneous oxidation of phosphorus which occurs on exposing 

 this substance to the atmosphere, ozone, 2 0, is always formed. As 

 a type of the formation of reducing substances in hydrolytic fermenta- 

 tions may be adduced the butyric acid fermentation, in which sugar 

 is converted into butyric acid, carbonic acid, and hydrogen : 



C 6 H 12 6 = C 4 H 8 2 + 2C0 2 + 2H 2 . 



The hydrogen produced in this process would act as a reducing agent. 

 There is no doubt that reducing substances are formed under normal 

 circumstances in the tissues, as is shown by the methylene-blue 

 experiment, and it is possible that such reducing substances may aid 

 in activating oxygen and in the induction of certain oxidative processes. 

 The activation of oxygen would, however, not explain the specific 

 character of the various oxidations, and the accurate gradation of these 

 oxidations to the necessities of the cell. In many cases reducing sub- 

 stances may themselves act as carriers of oxygen, and their action be 

 more or less specific. If, for instance, glucose be boiled with an am- 

 moniacal solution of cupric hydrate, it undergoes oxidation, the cupric 

 being reduced to cuprous hydrate. Cuprous hydrate in ammoniacal 

 solution is a reducing substance ; it absorbs oxygen from the air and 

 is reconverted to cupric hydrate. A small amount of cupric hydrate 

 therefore, in the presence of air, may act as a carrier of oxygen from 

 the air to the sugar and may thus oxidise indefinitely large quantities 

 of sugar. In the same way, if indigo in alkaline solution be boiled 

 with sugar, it undergoes reduction with the formation of a colourless 

 compound. On shaking the decolorised solution with air it absorbs 

 oxygen with the reproduction of indigo, so that here again minute quan- 

 tities of indigo blue may serve to oxidise large quantities of glucose. 

 The mode of action of these oxygen carriers resembles closely that of 

 the various ferments which effect the transference of water from the 

 menstrum to the substrate (e.g. trypsin, invertase, &c.). These 

 hydrolytic ferments differ from ordinary hydrolytic agents, such as 

 dilute acids, in the specific character of their action. Trypsin, for 

 instance, will hydrolyse polypeptides of a type corresponding to 

 those which make up the ordinary food- products, but is powerless to 

 hydrolyse polypeptides composed of artificial amino-acids which are 

 the optical isomers of those occurring in the body. It seems possible 

 that we might explain the specific oxidations occurring in the cell by 

 assuming the presence of a number of ferments, oxidases, which would 

 act as oxygen carriers, but each of which would only be able to act on 

 a certain type of food-stuff or on molecules of a given configuration. 



Such oxidative ferments have been described as existing in many 

 animal and vegetable extracts. Many species of fungus contain 



