220 GERMICIDAL SERA 



while the former is not. Whether the general enzyme is so changed 

 as to have specific action or a wholly new enzyme has been developed, 

 no one can say with certainty. Pfeiffer found that when a mixed 

 culture of the vibrio of cholera and another vibrio was injected into 

 the peritoneal cavity of a guinea-pig immunized to cholera, all the 

 cholera vibrios were dissolved and all the others were left whole. 

 When the same mixed culture was injected into the abdomen of a 

 guinea-pig immunized with the Nordhafen vibrio, all these were dis- 

 solved and the cholera vibrios left unharmed. The great majority 

 of bacteria are harmless because they are speedily destroyed by the 

 digestive secretions of the animal body. The germicidal constituent 

 of man's blood is easily made specific by vaccination with cholera 

 or typhoid bacilli. So far no specific bacteriolytic substance has been 

 developed in the blood of any animal with anthrax bacilli or strepto- 

 cocci. It is true that Pasteur developed highly efficient vaccines against 

 anthrax, but these increase phagocytic activity, probably through the 

 formation of opsonins, and do not develop immune sera. It will 

 be understood that we are not now concerned with toxin immunity. 

 We are confining ourselves to the study of specific bacteriolysins. 



It has been positively shown that the proteolytic enzyme which 

 destroys the bacteria is not an albuminous substance. Pfeiffer and 

 Proskauer precipitated a highly active cholera serum with alcohol 

 and allowed it to stand for three months with frequent change of 

 the alcohol. From the hard mass which formed, they extracted with 

 distilled water a highly active body which responded to none of the 

 protein reactions. Some serum preserved by the addition of 0.5 per 

 cent, phenol stood for ten years in Pfeiffer's laboratory and was found 

 to be active at the end of that time. The enzyme is not always so 

 susceptible to heat as was first supposed and some samples at least 

 require a temperature of 70 C. for one hour for complete inactivation. 



When a highly immune serum is injected into an animal it increases 

 its resistance to its homologous bacterium. Animals are actively 

 immunized by repeated treatments with the bacteria, either in attenu- 

 ated form or in small doses of the virulent form. Animals thus actively 

 immunized furnish an immune serum with which other animals may 

 be passively immunized. It is generally believed that living bacteria 

 give a better active immunization than dead cultures. Many years 



