11 225 



becomes inagglutinable after it has been heated to 115" for 20 minutes, while B. 

 coli communis loses little of its agglutinability at temperatures below 90°, and does 

 not lose it all even at 140°. 



Our own experiments (see Tables 11 to XI, Series 6 to 52) were conducted 

 partly with agar-cultures of various ages suspended in normal saline, and partly 

 with bouillon-cultures, and were designed to illustrate the change in the agglutin- 

 ability of B. coli produced by heat; experiments were also made with B. typhosus 

 for purposes of comparison. The object was to arrive at figures which would 

 express numerically the diminution in agglutinability caused by heating the suspen- 

 sion for a given time to temperatures varying from 40° to 100 , and also to find 

 the diminution in agglutinability consequent on heating the suspension to a given 

 temperature, to 70° or 100° for example, for longer or shorter periods. For all 

 temperatures under 100° the heating was done in a water-bath, which was grad- 

 ually raised to the required temperature and then left at that temperature as long 

 as was necessary. At 100° the heating was done in a Koch's steam sterilizer. All 

 the experiments of any particular series were carried out al the same time on the 

 same day, so that the values found in each series are directly comparable inter se- 

 Every care was taken to prevent any variation in the conditions of the successive 

 experiments from one day to another, or in the details of the heating of the bac- 

 terial suspensions or agglutinating sera. It should be noted that when either a B- 

 coli suspension in normal saline, or a bouillon-culture of it, is heated to 100° for even 

 15 minutes, it becomes less opaque. The longer this heating is continued the greater 

 is the loss in opalescence, so that after 6 hours at 100° the suspension is only half 

 as opaque as it was at first. Hence it seems to be best under these circumstances 

 to subject a strong suspension of the bacteria to the healing, and to dilute it to 

 the standard opalescence afterwards, when the effect of prolonged heating upon the 

 bacteria is being examined. 



It appears from these experiments thai temperatures below 60° diminish the 

 agglutinabilitii of the cultures but little, while lieating them to from 75° to 100° dimin- 

 ishes it very considerably. In most cases the loss of agglutinability is comparatively 

 small al 70°, the heated suspension requiring only 2 or 3 times as much agglutinine, 

 to produce a given degree of agglutination, as is needed by the unhealed culture; 

 but at 80° there is a sudden and considerable less of agglutinability, which falls to 

 Vio or V25 of its original value. Hence the agglutinability does not diminish regularly 

 as the temperature rises; it diminishes further, but not rapidly so, as the temperature 

 increases from 80° to 100°. In spite of all endeavours to obtain uniformity in all 

 the details and in the conditions of the experiments, it is at once obvious that the 

 results of the dilTerent series shew very considerable variations, and in spite of the 

 fact that the same agglutinating serum was used in all the experiments of Series 

 6 to 29. Yet we are unable to explain how it is that a 24-hour agar-culture of 

 our B. coli can give such widely varying results, from one day to another, when 



30' 



