The Conditions of Infusorial Life. 89 



hay in a pailful of water is more productive of the higher forms 

 of infusoria, than trials made in a tea- cup ; but we cannot ascend 

 by such experiments to the spontaneous production of the 

 mammoth from the general smash and corruption of older 

 families in the organic world. Tropical swamps exhibit some 

 of the conditions of vastness of decomposition,, which »M. 

 Pouchet considers essential to the exhibition of heterogenesis 

 on a grand scale; but can he show that they produce larger 

 creatures than would appear, if similar materials were operated 

 upon under the same atmospheric conditions in an experiment 

 of moderate size ? 



The state of division of the fermentable matter exercises a 

 considerable influence on the generation of infusoria, by hasten- 

 ing the chemical changes which make the fluid their fit abode. 

 Thus, a vessel containing water and chopped hay produced a 

 richer and different crop of animalcules, from another in which 

 the hay was in a mass. With respect to the influence of dif- 

 ferent sorts of water, M. Pouchet coincides with Burdach in 

 finding that of dew the most prolific; after which comes rain- 

 water, and then spring- water. He likewise observes, that water 

 which has been "boiled is less favourable to the production of 

 infusoria than the same fluid in its ordinary state. Such ob- 

 servations are easily explicable upon the theory of germs ; but 

 by adopting a singular process of reasoning, M. Pouchet endea- 

 vours to show that they support his own views. 



As mincing the fermentable material increased the produc- 

 tiveness of the fluid by accelerating decomposition, we should 

 expect a similar effect would, follow an increase in the supply of 

 atmospheric air ; and accordingly if two vessels are taken, and 

 in one chopped hay is kept near the surface, and in the other the 

 same substance is retained under a greater depth of fluid, the 

 first will exhibit the earliest, most numerous, and highly de- 

 veloped life. 



The prevalent theory of the distribution of germs supposes 

 the air to be the means of their dispersion, by first suspending 

 them, and then dropping them, wherever atmospheric dust falls. 

 It likewise appears, from numerous experiments, that a fresh 

 supply of air is necessary for the production of the higher forms 

 of infusoria, and that liquids in close vessels or/'y yield lower 

 kinds ; the probability being, that some of the gaseous products 

 of decomposition exercise an inimical effect, when they are not 

 permitted to escape. But although pure air may, with some 

 exceptions, be designated, with M. Pouchet, "indispensable to 

 the life of microzoaries," he discovered that the vacuum of an 

 air-pump did not destroy them. Fray and Burdach stated 

 that infusoria appeared in an atmosphere of hydrogen or nitro- 

 gen ; but M. Pouchet sums up the results of numerous experi- 



