400 J. RUSSELL ESTY 



thermal death point of the vegetative forms in human feces is 

 from 59° to 61°. In no case does a vegetative culture survive 

 63°, provided no spores are present. This is the temperature of 

 pasteurization. Using the data obtained from this work, fre- 

 quency curves showed no indication of more than one type in 

 this group. 



b. Spores. In the case of spores of Clostridium Welchii, there 

 seem to be two thermal death points, namely, either the cultures 

 resist 100° for fifteen minutes and longer or they die below 90°. 

 Some of the cultures survive 100° for thirty and forty minutes. 

 Two exceptions arise in the cases of number 11 and number 13 

 which fail to survive above 95°. Repeated tests confirmed the 

 failure of these strains to survive boiling. Spores from human 

 feces do not survive boiling in any case. Frequency curves show 

 conclusively that the thermal death points of spores fall into two 

 distinct groups. 



c. Relationship between vegetative forms and spores. An 

 inspection of the charts shows there is no correlation between 

 the thermal death points of the spores and the vegetative forms 

 for the thermal death point of vegetative forms may range from 

 56° to 60°, while spore forms of corresponding cultures resist 

 100°. Moreover, spores dying at 86° to 88° may resist 58° and 

 59° in the vegetative stage. It is impossible to predict the 

 thermal death point of the spore culture provided the thermal 

 death point of the vegetative culture for the same strain is known 

 or vice versa. 



d. Classification of sugar fermentation as compared to thermal 

 death points. The classification of the members of the Clos- 

 tridium Welchii group into four subgroups on a basis of the 

 fermentative reactions in glycerol and inulin, as shown in a 

 preceding section, bears no relationship to the two distinct 

 groups based on the thermal death points of spores. Each of 

 the four subgroups in the classification according to fermentation 

 contains members of both groups of thermal death points. The 

 same is true of the vegetative forms, each group containing 

 cultures whose resistance to heat varies widely. 



e. Relation of the time since isolation to the thermal death 

 point. Table 4 shows the effect of prolonged artificial culti- 



