200 THE FLOATING-MATTER OF THE AIE. 



It is worth bearing in mind that the particular kinds 

 of hay whose germs manifested these extraordinary- 

 powers of resistance were so sapless and indurated that 

 the specific gravity of their infusions, even after five 

 hours' digesting, could not without difficulty be sensibly 

 raised above that of distilled water. This was more 

 especially the case with old Heathfield and old Col- 

 chester hay, the infusions of which, though highly 

 coloured, were marked, almost without exception, 'spe- 

 cific gravity 1000.' Old London hay-infusion was 

 usually 1003, while infusions of new Heathfield hay 

 were raised without difficulty to 1007.^ 



As already stated, I never felt safe in these experi- 

 ments until they were checked by careful repetition. A 

 partial corroboration has been already adverted to. But 

 on the 2nd of March I had the same infusions prepared, 

 kept in a cool place throughout the night, and intro- 

 duced into four groups of bulbs next morning. The infu- 

 sions were all brilliant. During the process of boiling 

 one group of bulbs blew up, hence one link is absent from 

 the series. I thought the 4-hour group could be best 

 spared, and therefore selected it for omission. We had 

 thus the infusions subjected for one, two, three, five and 

 six hours respectively to the boiling temperature. The 

 three first hours agree exactly with their predecessors. 

 No single bulb within these limits was sterilized, all of 

 them became tm-bid throughout and loaded with scum. 



* A comparative experiment on dried and undried peas, de- 

 scribed in the Proceedings of the Royal Society (1877, vol. xxv. 

 p. 503), may be referred to here as illustrating the manner in which 

 desiccation restricts diffusion, and thus tends to preserve the in- 

 tegrity of the desiccated germ. I suppose the original mineral 

 salts of the hay were still retained in the old samples ; but hot 

 water appeared to have little power of extracting them. The resist- 

 ance of the hay in this respect appeared to be shared by its 

 germs. 



