134 SPONTANEOUS GENERATION. 



in either one of the four vessels, their germs being thus demonstrated to 

 have entirely subsided. 



In addition to the highly suggestive evidence adduced through these 

 several experiments, in demonstration of the persistency of form, and enor- 

 mous capacity for atmospheric diffusion, possessed by these monads, their 

 ultra-microscopic spores or germs are now shown to possess varying degrees 

 of ponderosity, and it would seem by no means beyond the range of possi- 

 bility, by further research, and having regard especially to the length of 

 time occupied in the subsidence of a given type, to ascertain, by comparison 

 with some larger and measurable variety, the exact or approximate dimen- 

 sions of those germs, as yet lying beyond the defining powers of our most 

 perfected microscopes, but instantly revealed by the searching electric beam, 

 and which may be cultivated at will in an appropriate fluid medium. 



In addition to the very important bearings upon the question of spon- 

 taneous generation embodied in the foregoing researches, Mr. Dallinger's 

 name demands notice also with reference to some most important experiments 

 conducted alone, and in combination with Dr. Drysdale, for the purpose of 

 ascertaining the power of resisting high temperatures possessed by these 

 lower forms of life in both their adult and sporular or germ condition. 

 These experiments entirely confirmed Professor Tyndall's observations, 

 and possessed, moreover, the additional advantage that a given and varying 

 thermal death-point, or limit of heat-resistance, was now associated for 

 the first time with fixed and specific monad types. Following out this 

 line of investigation, it was thus shown that the spores of Tetramitus 

 rostrata could successfully resist a temperature of 250 Fahr. (12 iC.), those 

 of Dallingeria Drysdali 220, those of Cercomonas typica 260, while in the 

 case of Heteromita rostrata and H. uncinata they passed unscathed through 

 a temperature of no less than 300 Fahr., or 148 C, which represents the 

 highest limit that has as yet been obtained. It was further ascertained that 

 a somewhat different result accrued according to whether the heat was 

 applied in a wet or dry form, the spores in certain instances exhibiting 

 a difference of as much as 10 Fahr. in this respect, and the highest 

 being resisted when applied in the dry condition. The adult and active 

 monads, having their constituent sarcode or protoplasm in a soft and semi- 

 fluid state, in all cases succumbed to the comparatively low temperature, 

 as an approximate limit, of 140 Fahr., and in many instances to one con- 

 siderably lower even than this. 



Some results of the author's personal investigations have now to be 

 submitted, which tend, from an entirely independent point of view, towards 

 the solution of the question now under discussion. Respecting Professor 

 Tyndall's highly valuable testimony, it has been, and may yet be, objected 

 by the partisans of heterogeny that his atmospheric germs are purely hypo- 

 thetical and intangible, not having been actually seen by him, nor, what 

 is more important, being so far connected with any recognized specific 

 form of infusorial life. The evidence adduced by Messrs. Dallinger 



