178 BACTERIOLOGICAL EXAMINATION OF WATER. 



sera, and to study how far the value of an anti-typhoid 

 serum is affected by the employment of several varieties (races) 

 of B. typhosus, either together or in succession. Ainley 

 Walker found that there was no cumulative action or 

 addition of agglutinating powers of the constituent monovalent 

 sera in the production of a polyvalent serum. That is to say, 

 the valency of polyvalent sera against any one of the varieties of 

 typhoid used in its production is neither greater nor less than 

 that of the monovalent serum obtained by the use of that 

 variety alone. Further, it appears that " the polyvalent serum 

 has no more powerful action on an independent variety of the 

 bacillus than the most powerful towards that bacillus of its 

 monovalent constituents." The " special "' agglutinative power 

 already obtained towards one variety of typhoid is found to 

 diminish when the injections are discontinued, in spite of the im- 

 munisation with another variety of the bacillus being continued. 

 For purposes of diagnosis either monovalent or polyvalent 

 sera may be used, though perhaps the latter would be more 

 generally useful. Ainley Walker found that polyvalent rabbits' 

 sera could be prepared which, when diluted in 1-3500, com- 

 pletely agglutinated the most pathogenic variety of the typhoid 

 bacillus against which it was tested. Horses'* sera, prepared 

 by immunisation extending over one year, when diluted 

 1-500,000 completely agglutinated the same variety of the 

 typhoid bacillus. Anti-typhoid monovalent. sera, prepared by 

 immunising rabbits and guinea-pigs for short periods, do not 

 usually bear dilution beyond 1-1000. It is quite easy to prepare 

 sera, which, when diluted 1-1000 will completely agglutinate the 

 B. typhosus ; but to obtain sera of greater strength requires 

 considerable time for the process of immunisation. Also, I have 

 found that " special "" sera, which act in a high dilution, slowly 

 lose their agglutinative action when kept at room tem- 

 perature. One serum in particular, which, when diluted 

 1-2,000,000 completely agglutinated different races of the 

 B. typhosus, slowly lost its agglutinative action, and at the 

 expiration of three months it ceased to influence the typhoid 

 bacillus when employed in a dilution above 1-10,000. 



Recognising these facts, it is important that every sample of 

 anti-typhoid serum shall be standardised with the stock cultures 



