226 12 



ils suspensions are exposed to heat and then agghitinated — see Series 6 to 15 — 

 unless it be the case (as was suggested on a previous page) that the discrepancies 

 are more apparent tlian real, and depend ujxju the inherent deficiencies of the 

 methods of measuring agglutinating power: at any rate they appear not to depend 

 ui)on dilTerences in the reaction of the suspensions used. It is to be noted that 

 the longer an cujar-cuUure has remained at 37°, the less is its agglutinahility impaired 

 by the action of heat, as the figures of Series 22 to 27 clearly shew: and also that 

 the first subcultures taken from a tube of B. coli that had been kept at the tem- 

 perature of the room for six weeks were comparatively little influenced by exposure 

 to heat. But this increased resistance to heat soon disappeared from the successive 

 subcultures made at short intervals from the original tube. If the influence of tem- 

 peratures between 4ü° and 100° upon agar-cultures and bouillon-cultures of B. coli 

 be more narrowly examined, it will be seen that there is an obvious ditTerence in 

 the behaviour of the two; the bouillon-cultures — see Series 28 and 29 — do not 

 give more uniform results, but illustrate the fact that agglutination can occur in 

 dilferent ways. When an agar-culture suspension has been heated to temperatures 

 between 40° and 100°, it often exhibits irregular agglutination and a zone where 

 agglutination has been inhibited, as is shewn by the fact that large amounts of the 

 immune-serum produce a less degree of agglutination than smaller amounts do; 

 this is exhibited in Series 10 to 14, 16 and 17, and 35 and 36. At the same time, 

 one frequently sees that quantities of serum that are insufficient to agglutinate the 

 unhealed suspension, will produce agglutination in it when it has been heated ; 

 while on the other hand the agglutination produced by a small amount of agglut- 

 inine may be equal to, or even greater than, that produced by a quantity 100 limes 

 as great, as can be easily seen in the experiments of Series 35 and 36, in which a 

 suspension of B. coli was warmed to 70^ for various times. 



These irregularities do not occur in most instances, or, if they do occur, it is 

 only to a small extent, when heated bouillon-cultures are used; see Series 28 and 

 29, and 38 to 42. On examining these irregularities more closely it is seen that they 

 do not depend upon the degree to which the agglntinubility of the bacteria is lowered. 

 For such "zones of inhibited agglutination" are often met with in cases wehere the 

 culture has only been warmed to 60° or 70°, and are absent where it has been 

 healed to 100°; but the opposite may be the case. And again, after the process of 

 agglutination has been proceeding for 2 hours at 37°, great irregularities may be 

 present in the degree to which it has taken place in a series of tubes; but 18 hours 

 later they will often have disappeared, partly or wholly, w-hile the tubes have been 

 standing at the temperature of the room. 



Thus there are a number of circumstances lending to prove Ihal when agar- 

 culture suspensions of B. coli are warmed, substances are formed tlud reduce the 

 velocity of the reaction of agglutination; but it is doubtful whether such a condition 

 of alïairs suffices to explain llie whole phenomenon. 



