1108 PHYSIOLOGY 



carriers of oxygen, and their action be more or less specific. If, for instance, 

 glucose be boiled with an ammoniacal 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 reproduc- 

 tion of indigo, so that here again minute quantities 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 menstruum 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 ammo-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 a ferment known 

 as tyrosinase, from the fact that, when it is added to solutions of tyrosine in 

 the presence of air, the tyrosine is oxidised with the formation of a brown 

 pigment. The same ferment is able to effect the oxidation of other aromatic 

 substances. The browning of a freshly cut potato or apple on exposure to 

 the air is similarly ascribed to the oxidation of a chromogen by the oxygen 

 of the air, through the intermediation of an oxidase present in the cells. 

 If benzyl alcohol or salicyl aldehyde be added to a suspension of liver-cells 

 in blood, and air be allowed to bubble through the mixture for some time, 

 the alcohol or aldehyde is oxidised to the corresponding acid. In the same 

 way xanthine (C 5 H 4 N 4 2 ) added to a mixture of spleen pulp and defibrinated 

 blood is converted into uric acid (C 5 H 4 N 4 3 ). 



Bach and Chodat have shown that in many cases the oxidase is not a 

 single substance, but a mixture of an organic peroxide with a ferment, 

 peroxidase, which has the property of splitting off atomic, i.e. active, oxygen 

 from the peroxide. These peroxidases have the same effect on hydrogen 

 peroxide. They must be distinguished from the ferment catalase, which is 

 present in almost all animal and vegetable tissues, and which effects a rapid 

 decomposition of hydrogen peroxide with the formation of molecular 

 oxygen : 



2H 2 2 = 2H 2 O + O 2 . 



