INFECTION AND IMMUNITY. 571 



material of animals immune from bacterial and other 

 toxins. Since the announcement of that doctrine many 

 important advances have been made in our knowledge of 

 the subject. We have learned that immunity or tolerance 

 may be induced by the use of other intoxicants than those 

 elaborated by bacteria, and by the employment of other 

 cells and cell secretions. It has been demonstrated that 

 anti-bodies, differing in their specific actions from anti- 

 toxins, but originating probably in a similar manner, are 

 to be detected in the fluids of animals thus immunized or 

 rendered tolerant. For a long time we have known of 

 the germicidal action of normal blood-serum ; since 1895 

 we have been familiar with the singular bacteriolytic 

 phenomenon demonstrated by Pfeiffer in the peritoneum 

 of animals immune from cholera ; more recently we 

 have learned that immunity from a variety of infections 

 is accompanied by a power on the part of the serum of 

 the immune animal to agglutinate the bacteria causing 

 the infection ; the work of Wright upon his opsonic 

 doctrine has finally placed the leukocyte among the im- 

 portant defenses of the body and the profoundly inter- 

 esting investigations of Bordet, Moxter, von Dungern, 

 Fish, and others, have shown that immunity may be in- 

 duced from cells and secretions of animal origin hitherto 

 regarded as non-irritating and harmless. For instance, 

 we have learned that the blood of one animal may cause 

 fatal intoxication when injected into an animal of dif- 

 ferent species; but if that blood be repeatedly injected 

 in non-fatal amounts, the animal receiving the injections 

 after a while becomes tolerant, and its serum reveals the 

 property not only of robbing the alien blood of its 

 hurtful properties, but also of actually dissolving its 



