EMULSOIDS 307 



derma aceti, the bleaching of indigo solution by hydrogen 

 peroxide in presence of red blood corpuscles, the blueing of 

 tincture of guaiacum by hydrogen peroxide in presence of red 

 blood corpuscles, etc., all of which can also be affected by 

 spongy platinum. 



Bredig carried our knowledge of the subject a step farther ; 

 by preparing colloidal solutions of the metals and comparing 

 their action with that of various enzymes, he traced out such 

 a remarkable analogy between the two that he has called the 

 colloidal metal solutions " Inorganic Ferments ". 



The chief points of similarity between enzymes and 

 colloidal platinum may be summarized as follows : 



1. Both platinum hydrosol and enzymes are colloids and 

 as such are detrimentally affected by electrolytes. 



2. Both platinum hydrosol and enzymes gradually de- 

 compose spontaneously or decompose more rapidly by heat- 

 ing. 



3. There is an optimum temperature for both colloidal 

 platinum and for enzymes to exert their catalytic action. 



4. The activity of platinum hydrosol may be stimulated 

 by the addition of alkali until it reaches its maximum value, 

 after which the further addition of alkali causes it to fall again. 

 Similar stimulation of enzymes by the addition of certain sub- 

 stances known as Zymo-exciters have been observed in case 

 of emulsin acting* on hydrogen peroxide, and of invertase 

 acting on cane sugar. 



5. The decomposition of hydrogen peroxide whether by 

 platinum hydrosol or by haemase, the enzyme contained in 

 blood, is in accordance with the laws governing a monomo- 

 lecular reaction. 



6. A very remarkable analogy between platinum hydrosol 

 and the enzyme of blood is that small quantities of substances 

 which, when added to the colloidal platinum solution, destroy 

 its catalytic action on hydrogen peroxide, also have the same 

 effect on the oxidase of blood. Curiously enough many of 

 these substances are blood poisons such as sulphuretted hydro- 

 gen, hydrocyanic acid, carbon monoxide, and arseniuretted 

 hydrogen ; several other substances were also found to para- 

 lyse either the platinum solution or the enzyme. 



It was further observed that platinum hydrosol when 



20* 



