I 2 4 SPONTANEO US GENERA TION. 



with those of the higher animals,' and which circumstance he declared ren- 

 dered the addition of an independent or spontaneous mode of growth 

 entirely superfluous. Evidence of a far more substantial nature, and which 

 was held at the time to be utterly subversive of the cause of the heterogenists, 

 was that produced by Schultze and Schwann in the years 1836 and 1837. 

 The former of these demonstrated that organic infusions after boiling might 

 be exposed to the action of the atmospheric air for many months without 

 developing living animalcules, provided such air passed first through con- 

 centrated sulphuric acid, which was pronounced by Schultze to destroy 

 or devitalize the air-suspended germs. The results obtained by Schwann 

 and the means employed were precisely identical, excepting that calcined 

 air was substituted by him in place of sulphuric acid. An important con- 

 clusion arrived at by this investigator, as a necessary corollary of the above 

 results, was, that the putrefaction of organic bodies was entirely dependent 

 on the associated growth and multiplication within their substance of 

 minute organisms, such as Infusoria and their allies. 



Helmholtz in the year 1843, and Schroder in various contributions pub- 

 lished between the years 1854 and 1859, accumulated additional evidence 

 in favour of the panspermists, and towards demonstrating that the animal- 

 cules developed in infusions originated mainly, if not entirely, from pre- 

 existing atmospheric germs. Among the more noteworthy experiments 

 of Helmholtz, it was shown that a putrefying infusion, and one sterilized 

 by boiling, might be divided from each other by means of a thin membrane 

 only, so that the liquid masses of the two might freely intermingle through 

 the processes of exosmosis and endosmosis without the latter one becoming 

 tainted, as it indubitably did if the smallest portion of the putrescent fluid 

 was added to it in its concrete form. The unavoidable conclusion derived 

 from this experiment was that the germs existed in the putrescent infusion 

 as actual very minute and solid particles that could not pass like the asso- 

 ciated fluids through the intervening membrane. Following out this same 

 line of demonstration, Schroder further showed that simple plugs of cotton- 

 wool inserted in the necks of flasks containing organic infusions sterilized 

 by boiling, sufficed as efficient filters for the exclusion of organic germs, 

 and for the indefinite maintenance of the liquid in the sterilized condition. 

 This last-named experiment is now commonly repeated ; flasks of steril- 

 ized putrescible fluid being at the present moment on view at the South 

 Kensington Biological Laboratory, which have remained for many years 

 with a similar simple cotton plug guarding their contents from the invasion 

 of organic germs and accompanying putrefaction. 



Notwithstanding the almost overwhelming amount of evidence now 

 adduced in contravention of the hitherto extensively upheld doctrine of 

 spcntaneous generation, a new champion of its cause was soon to the fore- 

 front, and one who has almost down to the present day laboured with all 

 his force and much ingenuity to prove his case. This new leader of the 

 heterogenists was no other than Dr. F. A. Pouchet, the accomplished 



