222 SPECIFIC NATURE OF CATALYTIC ACTION 



of the incubation period depends upon the period of reaction of 

 the tissue cells, and not upon any cycle of development of the 

 parasite as, for example, in enteric fever, where the Bacillus 

 typJiosus possesses no period of growth corresponding to the period 

 of incubation. 



Finally, variations in immunity in different individuals here, 

 equally as in parasitic infection, will depend upon the individual 

 variations in the blood as a suitable medium for such a reaction, 

 upon the presence or absence of an antibody at the outset capable 

 of neutralising the trace of autocatalyst bearing the infection, and 

 upon the reactive power of the tissue cells to the autocatalyst or 

 toxin. 



THE SPECIFIC NATURE OF CATALYTIC ACTION. 



It has already been mentioned that enzymes are very specific 

 in their action, and in the character of the products which they 

 produce from the substratum. 



It has been well pointed out by Bredig that this cannot be 

 converted into a criterion for distinguishing the action of an 

 enzyme from that of an inorganic catalyst. For although such 

 specific action is seen at its maximum in the enzymes, it is also 

 observable in the action of many inorganic catalysts. Thus while 

 certain catalysts, such as the hydrogen ion, are very general in 

 their action, catalysing most hydrolytic reactions, such as cleav- 

 age of all disaccharides, amyloses, and esters, other catalysts are 

 quite selective in action. Examples quoted by Bredig are potassium 

 bichromate, which energetically catalyses the oxidation of hydriodic 

 acid by bromic acid, but does not act upon that of the same acid 

 by iodic acid or potassium persulphate; iron and copper salts, 

 which intensely catalyse the oxidation of potassium iodide by 

 potassium persulphate, but not the oxidation of sulphurous acid 

 by the same oxidising agent. 



On the other hand, as also pointed out by Bredig, emulsin 

 in addition to hydrolysing the glucoside amygdalin with which 

 it is naturally associated, similarly acts upon many other sub- 

 stances, such as arbutin, helicin, salicin, phloridzin, daphnin, 

 coniferin, aesculin, and lactose. 



There is no doubt, however, although no fundamental difference 

 can be deduced therefrom, that the vast majority of the enzymes 

 are more highly selective in their action than the inorganic enzymes. 



