342 



Kev. W. H. Dallinger on 



[May 2, 



between nine and ten hours, but their number was far fewer than in 

 those instances where a lower temperature had been employed. 



I followed this with four more experiments, separately and succes- 

 sively made. Two of them were at a temperature of 248°, and two at 

 252° F. In both of the former, at the end of nine or ten hours, the 

 complete organism in full vigour could be seen ; and, in one of the cases, 

 it was discovered in the still condition shown at fig. 20, Plate 9, and 

 watched until the organisms had attained the condition indicated in 

 fig. 24, Plate 3. 



But in the two latter instances (heated up to 252°) the living form 

 did not re-appear during the six days following, although repeatedly 

 looked for. 



I concluded, therefore, that the temperature of 250° P. was the 

 limit of endurance which the spore of this form could bear by this 

 method of heating. 



Now, it must be noticed that in testing the death-point of the 

 adult, as I shall presently show, a fluid heat was employed. But the 

 spore can hardly be said hitherto to have been heated in the same con- 

 ditions. Doubtless, in the heating chamber the higher temperatures 

 are endured after evaporation, and consequently the heat is " dry.'' 

 But after years of thought on the matter, no other way has suggested 

 itself to me as possible, for the attaining of the result, by other means. 

 What is required is, that we should know beforehand, that in the drop 

 of fluid exposed to a given heat, the spores of a given organism in a 

 freshly emitted condition, and, therefore, before development had begun, 

 were present. And, moreover, that it should be so placed that after 

 heating it should be in such conditions as would admit of the use of 

 the highest power lenses to discover if the spores, known to have been 

 deposited there, would, after subjection to the thermal conditions 

 given, develop as they had been demonstrated to do before heating. 



Now, there are two ways of doing this. The one is approximate. 

 It is by long and intimate acquaintance with the history of the 

 organism, and a careful and close study of the condition of the fluid — 

 by which means it is possible to come very near to the highest proba- 

 bility — that the spores in the required condition are there. But in this 

 case negative results must be extremely perplexing. The other way is 

 to see the spores actually emitted in the drop of fluid that is to be 

 heated. This is the only certain method ; it is most exhausting and 

 laborious, but its results are certain, and therefore I have employed it 

 in this case. But to adopt the supposition which Dr. Bastian has 

 recently done,* that to heat a given monad spore in a given condition 



* On the Conditions Favouring Fermentation, &c., " Linnean Soc. Jour.," vol. xiv. 

 This paper contains some curious inaccuracies of statement as to facts — evidently 

 the results of misapprehension on Dr. Bastian's part — concerning the result? of 

 thermal experiments made by Dr. Drysdale and myself on the Monads. These occur 



