27 241 



amounts of acid are present, fluctuations in their value exert a very powerful in- 

 fluence upon the agglutination produced by an immune-serum. 



Ta))les XXVII to XXXI record the results obtained when the serum is lirsl 

 treated with an acid and then neutralised. They shew that, speaking generally, 

 the "zones of inhibition" and the increased agglutinating power both disappear on 

 neutralisation. With reference to the diminution that sometimes occurs in the 

 agglutinating power, it is to be observed that when comparatively small amounts 

 of the acid have been employed, the return of agglutinating power to the serum on 

 neutralisation is almost complete ; but that if larger and larger quantities of the 

 acid are allowed to act upon the serum and the mixture is then neutralised, the 

 reduction of the agglutinating power does grow progressively greater and gi'eater. 

 Still, a part, at least, of the agglutinating power always returns (within wide limits, 

 that is to say), where neutralisation is performed. 



In the same way the velocity with which the agglutination takes place is very 

 considerably diminished when the immune-serum has been treated, before neutral- 

 isation, with tolerably large quantities of HCl — with '•'U normal HCl, for example. 

 The figures set down in Series 88 and 89, where the serum was treated with 

 2283 per cent HCl, shew that after the neutralised serum had acted for IV2 hour 

 at 37° upon the bacterial emulsion, its agglutinating power appeared to be only 

 '/i7 and V?, in the two cases respectively, of that of the untreated serum. The 

 same test-tubes, examined 18 hours later, shewed that their powers were by that 

 time only reduced to V5 and V2 of what they had been before they were acidified. 



All of the observations quoted above were made upon agar-culturc suspen- 

 sions of B. coli. 



The results obtained from Iniiiillon-ciiltiires are both qualitativeli) and quantitatively 

 different. This is shewn to be the case by the i-esults of experiments made simul- 

 taneously upon the same day and with identical dilutions of the immune-serum, 

 so that they are as strictly comparable one with another as is possible. 



It is made evident in Tables XXV, XXVIII, and XXIX, Series 79, 80, and 84 

 to 87, that with bouillon-cultures, the "zones of inhibited agglutination" are a less 

 prominent feature. They do not occur unless the serum has been treated with very 

 considerable quantities of acid — cjuantities that are perhaps 20 or 30 times as 

 great as those required to produce "zones" when the agar-culture suspension is 

 employed. None the less, however, the agglutinating power of the immune-serum 

 may be reduced to V19 of its original value under such conditions as these ^— see 

 Table XXV, Series 80. 



But if the acidified serum is neutralised before use with the bouillon-cultures, 

 it becomes apparent that in this case also the loss of its agglutinating power is to 

 some extent apparent rather than real; for with neutralisation, the serum recovers 

 its agglutinating power to a large extent or even entirely. 



32* 



