POUCHET ; PASTEUR. 125 



Director of the Rouen Natural History Museum. In the year 1847 Pouchet 

 had already demonstrated that the multiplication of Infusoria by the 

 process of fission was by no means so common as was ordinarily supposed, 

 and that the astonishingly rapid increase of their numbers could not be 

 accounted for by such simple means. It was not, however, until the year 

 1859 that he brought forward that new interpretation of their developmental 

 phenomena with which his name is most eminently associated. In accord- 

 ance with the representations of this author, the most important factor in 

 the production of animalcules, independent of parental agency, or in other 

 words by spontaneous generation, was the filmy or gelatinous skin or 

 pellicle, that within a greater or less interval is commonly developed on the 

 surface of putrefying infusions. According to Pouchet this superficial 

 pellicle, designated by him the pseudo-membrane, or "proligerous mem- 

 brane," was the matrix, produced through the decomposition or breaking 

 down of pre-existing organisms, in which egg-like bodies were generated 

 de novo and developed into various species of Infusoria. The idea of 

 the germs existing in the atmosphere in sufficient quantities to produce 

 their normal and remarkably rapid development, as held by the pan- 

 spermists, was rejected by Pouchet as not only untenable, but ridiculous, 

 he reasoning that if such abundance obtained, they would visibly interfere 

 with the clearness of the atmosphere and produce masses comparable with 

 the clouds themselves. 



The arguments of Pouchet were not destined to remain long unchal- 

 lenged. In the following year, 1860, M. Pasteur, the eminent chemist of the 

 Parisian Conservatoire, entered the lists on behalf of the panspermists, and 

 after several years of animated controversy with Pouchet and his partisans, 

 accompanied by the most patient and ingenious experiments, achieved 

 results that most completely turned the tables upon the heterogenists. 

 Among the more prominent and positive of these must be mentioned 

 Pasteur's actual collection of floating organic germs, mingled with inorganic 

 particles from the atmosphere, and which sown by him in sterilized infusions, 

 were found to develop the ordinary infusorial animalcules in abundance. 

 It was further demonstrated by the same investigator that the atmo- 

 spheric germs in question were by no means so evenly and abundantly 

 distributed as the panspermists had previously maintained. Thus, while 

 sterilized infusions became immediately affected, and crowded with animal- 

 cules, when exposed to the grosser and comparatively impure atmosphere 

 of large towns, or other thickly peopled districts, he showed by direct 

 experiment that the same infusions bore the ordeal of exposure to the clear 

 and moteless atmosphere of the Alpine glaciers without exhibiting the 

 slightest alteration or trace of organic life. Transporting his experimental 

 flasks to the pure and tranquil air of those subterranean vaults or " cata- 

 combs " for which Paris is so famous, a similar exemption from organic 

 change was observed. In a still more complete and precise manner, Pasteur 

 also repeated and confirmed the experiments of Schwann and Schroder 



