96 PHYSIOLOGY OF ALIMENTATION. 



prevent overheating of the water, as this causes the platinum, 

 gold, silver, or whatever metal is being employed, to be 

 precipitated. In other words, the inorganic ferment is 

 destroyed. For this reason, therefore, the dish of water 

 in which the colloidal solution is being prepared is kept 

 cooled with ice, and overheating by allowing the electric 

 current to pass through the water for too long a time is 

 carefully avoided. It,' was pointed out above that the de- 

 composition of the true ferments by heat might represent 

 nothing but a physical change. For, as far as we know now, 

 the organic ferments are all colloidal solutions, and in con- 

 sequence exceedingly liable to precipitation (and inactiva- 

 tion) through heat. The greater sensitiveness to heat in the 

 case of the true ferments is readily explained on the ground 

 that these are always impure mixed with salts, etc., from 

 which it is impossible to free them and consequently more 

 readily precipitated. As will be shown in greater detail 

 further on, the presence of certain impurities, such as gases 

 and salts, in the colloidal solutions of platinum greatly 

 decreases their stability also. Colloidal solutions of platinum, 

 gold, etc., are the more readily precipitated (destroyed) by 

 heat the greater the amount of these impurities. It may 

 be for this reason that the purest ferments which have thus 

 far been obtained are least sensitive to temperature. Whether 

 inorganic ferments have an optimal temperature as do th 

 true ferments is not yet worked out sufficiently. The recent 

 work of ERNST l shows that such a temperature exists in 

 the case of the decomposition of oxyhydrogen gas in aqueous 

 solution in the presence of colloidal platinum. 



It was held for a long time that the inorganic ferments 

 differed from the organic in one essential detail. While the 

 action of the ordinary ferment comes to a standstill after a 

 certain time, a reaction catalyzed by an inorganic ferment 

 seemed always to be complete. It was shown above that 



1 ERNST: Zeitschr. f. physik. Chem., 1901, XXXVII, p. 448. 



