220 AUTOCATALYSIS AND INFECTION 



laccase, and of calcium salts in increasing the rapidity of action 

 of the coagulating enzymes, may also be mentioned in this con- 

 nection. 



In inorganic reactions examples of similar effects are seen in 

 the action of minute traces of copper salts in aiding the catalysis 

 of hydrogen iodide and hydrogen peroxide by iron salts, and in 

 the action of traces of alkali in increasing the power of colloidal 

 platinum solutions upon hydrogen peroxide. 



AUTOCATALYSIS AND INFECTION. 



In the course of any reaction the products formed may them- 

 selves in certain cases act as catalysts and alter the velocity of 

 the reaction. For example, in the hydrolysis of esters by water, 

 the process is at first so slow as to be inappreciable, but as the 

 process goes on, the hydrogen ions of the acid set free in the reaction 

 itself act as a catalytic agent upon the portion of ester still un- 

 decomposed and hasten the reaction. To such a process Ostwald 

 has assigned the term of " autocatalysis," and has pointed out 

 that such a process may play an important role in biological pro- 

 cesses, and that the course of such autocatalytic reactions bears 

 a close analogy to the phenomena of fever. 



If the substance produced acts as a negative catalyst it will 

 have only the effect of making the reaction run more slowly, and 

 as its effect will increase with rising concentration, the result will 

 be that the course of the reaction will resemble that of an ordinary 

 reaction, save that the tendency to run more slowly as the equili- 

 brium point is approached will be increased. 



When, however, the substance formed in the reaction acts as 

 a positive catalyst, the course of the reaction becomes markedly 

 changed in a most interesting fashion. 



For while in the ordinary non- catalysed reaction, or a reaction 

 in which the concentration of catalyst remains constant, as in 

 all those which we have previously considered, the velocity of 

 reaction diminishes steadily onward from the beginning, in an 

 autocatalytic reaction, as the quantity of autocatalyst increases 

 as the reaction proceeds, the reaction is correspondingly hastened. 

 Hence a reaction of this type may begin by being barely perceptible, 

 but gathering way as it proceeds like a descending avalanche, 

 may in the end become stormy or explosive. 



