172 INFECTION AND IMMUNITY. 



of acquired immunity may be referable to differ- 

 ences in the character of the cell receptors at dif- 

 ferent ages, while perhaps others are due to a slow 

 immunizing process occasioned by the prolonged 

 presence of non-pathogenic amounts of the proper 

 micro-organisms. 



Enzymes. Emmerich and Loew found that many bacteria 

 produce in culture media, as well as in the animal 

 body, substances which apparently act as ferments 

 and which are able to kill not only the bacterium 

 which secretes the ferment, but many others. For 

 example, pyocyanase, the bacteriolytic enzyme of 

 Bacillus pyocyaneus, dissolves pyocyaneus, 

 anthrax, diphtheria and typhoid bacilli, the vibrio 

 of cholera, the streptococcus and staphylococcus. 

 These enz} 7 mes usually are not toxic, and it has 

 been supposed that in the course of an infection 

 they reach such a concentration in the blood that 

 they destroy the bacteria which produced them, 

 thus bringing about recovery. It is asserted also 

 that they, either during infection or as a result of 

 repeated injection of the ferment, enter into a 

 somewhat permanent combination with the al- 

 bumin of the body, forming the so-called "im- 

 mune-proteidins," on which acquired immunity 

 depends. 



It is also stated that with "pyocyanase-immune- 

 proteidin" it is possible so to immunize a rabbit 

 that a subsequent (twelve days) otherwise fatal 

 dose of the anthrax bacillus is harmless. 



Although the effects of these "enzymes" on 

 anthrax and on some other organisms have been 

 confirmed by a number of investigators, their im- 

 portance in acquired immunity and in the recov- 

 ery from infections is very doubtful. There is the 



