ON IMMUNITY TO BACTERIA 337 



infections, already alluded to, now requires further mention. It 

 is obvious that the role which it plays varies greatly in different 

 diseases. There is, for instance, no evidence for believing that 

 the blood ever develops any substance which is bacteriolytic for 

 the tubercle bacillus. It is true that the researches of Wassermann 

 and his coadjutors show (by means of the method of fixation of 

 complement) that an antibody may occur in tuberculosis or in 

 tuberculous animals, but there is no evidence that this is a 

 bacteriolysin, or, if so, that it ever occurs in amounts sufficient to 

 bring about solution of tubercle bacilli ; in fact, it appears probable 

 that tubercle may run its whole course without leading to the pro- 

 duction of any recognizable antibody. So, too, with staphylococcic 

 infections. Here it is possible by special methods to produce a 

 serum which has a slight bactericidal effect, but normal human 

 serum or the serum of a patient who has been submitted to a 

 course of antistaphylococcic vaccination is quite powerless in this 

 respect. It is obvious, therefore, that neither the high grade of natural 

 immunity to staphylococci of normal persons nor the increased 

 amount present in active immunity is due to any bactericidal or 

 bacteriolytic substances occurring in the blood. It is quite true 

 that in old specimens of staphylococci pus-free cocci in all stages 

 of degeneration can be found, rendering it quite obvious that a 

 process of extracellular death and destruction of bacteria is at 

 work. This phenomenon is probably to be attributed mainly to 

 the action of the proteolytic enzymes formed by the leucocytes of 

 the pus. These are substances which are too often neglected in con- 

 sideration of immunity. They are, of course, non-specific, and will act 

 on any dead proteid, and on some living organisms. Their action may 

 be demonstrated by allowing some liquor puris from an old abscess 

 to act (in presence of thymol) on some staphylococci which have 

 been previously boiled to prevent autolysis. Another process in 

 which these degenerated forms of cocci may be produced is by 

 spontaneous autolysis in organisms killed by lack of suitable 

 nourishment, or atrepsy. 



In sharp distinction from tubercle and the staphylomy coses, we 

 find such diseases as cholera and typhoid fever, in which bacterio- 

 lysins are formed in large amounts, and are readily demonstrable 

 by simple methods. It is in these and a few other diseases that 

 we may expect the role of these substances in recovery and 

 immunity to be most marked. We find, however, that their 

 action is most difficult to understand, and that its importance 



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