418 THE BEGINNINGS OF LIFE. 



a vessel which is full nay, more, in one in which they 

 are cut off from all access of light. My flasks, on the 

 contrary, have been only half filled with the fermentable 

 infusions, and these have been subjected to any 

 disturbing influences which may have been derivable 

 from the influence of light, at the same time that they 

 have been purposely exposed to a warm temperature. 



What, then, is the explanation to be given of the 

 results which I have obtained ? Quite early in the 

 present century Gruithuisen discovered, as we have pre- 

 viously quoted from Burdach, that c infusions, otherwise 

 very prolific (those of hay, for example), did not yield 

 infusoria in glass vessels in which the stopper touched 

 the surface of the fluid.' Under such circumstances \ 

 no space is left for the liberation of waste gases ; 

 pressure rapidly increases, and fermentative or putre- 

 factive changes, if they chance to be initiated at all, 

 are generally checked at their very onset 2 . When 



1 Even Gay-Lussac was also aware of a similar fact with regard to 

 urine. And, moreover, urine may often be preserved, in this way, when 

 it has not been previously boiled. 



2 A microscopical examination of the surface of some preserved meats 

 which are sold as being ' perfectly good,' and whose taste ratifies the 

 truth of this description, has occasionally revealed the presence of a 

 number of Bacteria and Leptothrix filaments, which, though extremely 

 small in quantity and not numerous enough to affect the quality of the 

 provisions, would seem to have been developed in the situation in which 

 they are found, because the meats in their original condition do not 

 present even this amount of organisms, and because other cases 

 of meats are found to be perfectly free from organisms (' Nature,' No. 48, 

 p. 433). Thus a change seems to commence in certain cases, which is, 

 however, so speedily stopped (owing to the unfavourable nature of the 



