BACTERIOLYSIS AND ALLIED PHENOMENA 



amount of antibody present is estimated. In the case of anti- 

 typhoid serum the simplest method is to measure the degree of 

 agglutination, which may rise as high as i : 1,000,000. This 

 cannot be taken as an absolute criterion of the amount of bactericidal 

 substance present, but in the great majority of cases the two 

 antibodies are developed roughly proportionately, and the agglu- 

 tination may be taken as a fair guide. Of course, the bacteriolytic 

 potency may be worked out by the method already described, 

 taking care that a sufficient amount of complement is added, and 

 that there is no deviation. This is probably the best method, and 

 is sometimes employed; thus Shiga found that 0*0001 c.c. of his 

 antidysentery serum when reactivated by 0-3 c.c. of fresh serum 

 would kill all the bacilli in T J^ milligramme of a one-day-old agar 

 culture. 



The results of tests of this nature have been to show that 

 extremely potent sera can be obtained against typhoid bacilli, 

 cholera vibrios, dysentery bacilli, and perhaps streptococci ; sera 

 of less but still of some power against plague bacilli, anthrax 

 bacilli, pneumococci, the gonococcus, and the meningococcus ; 

 whilst the results with staphylococci and tubercle bacilli have 

 been to all intents and purposes negative. 



The method of action of these sera is not quite settled. In 

 some cases there is an abundance of bactericidal immune body, 

 and there is no reason to doubt that, when employed as a prophy- 

 lactic agent, this becomes complemented in the animal body, and 

 causes bacteriolysis of the infecting organism. This is certainly 

 the case with the sera directed against typhoid fever, cholera, and 

 dysentery. In other sera, which are, nevertheless, of definite 

 protective and even curative value, this effect cannot be demon- 

 strated. This is the case with anti-anthrax serum. Here we 

 have to assume either that the substance owes its value to the 

 presence of opsonins or of anti-endotoxin, or possibly (in some 

 cases) that it may contain free toxins, or at least specific antigens, 

 and act as a vaccine, producing active rather than passive 

 immunity, as was suggested by Wright in the case of Calmette's 

 typhoid serum, which is prepared in a manner somewhat different 

 from that just described. There is some reason for thinking that 

 Sclavo's serum acts opsonically, and with regard to the presence 

 of anti-endotoxin, it may be pointed out that the prolonged course of 

 immunization usually employed may lead to the production of 

 this substance in small amounts. 



