10 



OVUM. 



servers* placed in a glass flask an infusion of 

 organic matter, a portion of which was known 

 from comparative trials, when left exposed to 

 the open air, soon to have animalcules deve- 

 loped in it in great quantity, and he connected 

 this vessel with a tubular apparatus, by two 

 apertures, in such a manner that the air, which 

 was made to pass frequently through the 

 vessel containing the infusion, should be drawn 

 through strong sulphuric acid, or potash solu- 

 tion, before reaching it ; and Schwann | ar- 

 ranged a similar experiment, having in view to 

 secure the like conditions, by causing the air, 

 which had access to the infusion, to be pre- 

 viously passed through an iron tube at a red 

 heat. Before the commencement of these 

 experiments, the infusion and the apparatus 

 were carefully subjected to the temperature 

 of boiling-water, by which it was presumed 

 the vitality of all ova, or germs, or other or- 

 ganic particles must have been destroyed : 

 and the result was the same in both the series 

 of experiments, viz., that, after a consider- 

 able lapse of time, no animalcules nor con- 

 fervoid plants were formed : but when the 

 atmospheric air was afterwards allowed to 

 pass freely over the same infusion, without 

 being subjected to the processes before men- 

 tioned, a rapid production of infusory ani- 

 malcules took place in the usual manner. 



The results of these experiments appear to 

 be on the whole satisfactory, and nearly to 

 decide the question as far as relates to the 

 probability of the introduction of the germs 

 of Infusoria, &c., into infusions by the air. 

 But, indeed, the failure of many experiments 

 of this kind, when not performed with the 

 most scrupulous accuracy, need not excite 

 surprise, when the very indestructible nature 

 of some kinds of infusory animalcules is con- 

 sidered. It has long been known, and has 

 been ascertained by the careful experiments 

 of Spallanzani, Bauer, and Doyere, that some 

 of the Rotifera and Tardigrada are capable of 

 supporting a high temperature without loss of 

 life, and of being kept for years even in the 

 state of complete dryness, without loss of 

 vitality : and, although it must be admitted 

 that these animals differ greatly in their or- 

 ganisation from the Polygastric Infusoria, and 

 the latter appear to be very liable to destruc- 

 tion from slight causes, yet it is possible that 

 their germs may resist destruction in a greater 

 degree than their adult forms : and, should 

 only one of these animalcules, or its germ, 

 be left in any situation favourable to its 

 development, it is easily understood, from 

 what is known of the production of these 

 beings, with what rapidity a vast multitude 

 of them may be brought into existence by 

 their ordinary process of fissiparous increase. 



Most physiologists are inclined to reject as 

 fanciful and inaccurate the alleged observa- 

 tions of the actual conversion of particles of 

 organised or organic matter into living in- 



* Poggendorff's Annalen, 1837, and Edin. New 

 Phil. Journ. vol. xxiii. p. 165. 



t In paper on Fermentation, &c. in Poggen- 

 dorff's Annalen, 1837, p. 184. 



fusoria. At all events, statements of this 

 kind are to be received with the greatest 

 caution : such, for example, as the observa- 

 tions stated to have been made by Pineau*, 

 who affirms that he has seen the direct con- 

 version of particles of disintegrating muscular 

 fibre, isinglass, and wheat-flour, into various 

 forms of living infusoria. 



The spermatic filaments also, which, so 

 long as they were looked upon as independ- 

 ent animals, were referred to as examples of 

 an undoubted spontaneous generation, furnish 

 no evidence in favour of that hypothesis in 

 the view in which they are now regarded by 

 physiologists : for they are to be considered 

 rather as a peculiar product of organic growth 

 within the spermatic cells, somewhat ana- 

 logous to the fine moving processes of the 

 ciliated texture, than as distinct organisms, -f- 



In so far, therefore, as the theory of spon- 

 taneous generation may have been supposed 

 to derive support from the formation of the 

 lower forms of plants and animals in infusions 

 of organic matter, that hypothesis must be 

 considered as having lost the greater share of 

 its probability, if, indeed, it has not been 

 entirely disproved : but it must at the eame 

 time be admitted that a more precise ac- 

 quaintance with the nature of the germs from 

 which these organisms take their origin is 

 still required to render the arguments derived 

 from this source entirely conclusive.^ 



The external and internal parasites which 

 infest the bodies of almost all animals have 

 in former times been held to afford a still 

 stronger presumption in favour of sponta- 

 neous generation than the production of in- 

 fusoria ; but it will be found that in this 

 instance, to a much greater extent than in the 

 other, the probability of the view has gradu- 

 ally passed away before the increasing know- 

 ledge which modern research has afforded of 

 the various modes of propagation of these 

 animals. 



The ready communication of various Epi- 

 zoa, or external parasites, from one animal to 

 another is now well known, and accurate ob- 

 servations have demonstrated that in almost 

 all instances this communication may be 

 traced to the implantation of ova, or pregnant 

 individuals into their parasitic abode, as in 

 the researches on the Sarcoptes scabiei, &c. 



The parasitic fungi, also, of various cuta- 

 neous diseases, as tinea, porrigo, plica po- 

 lonica, foul ulcers, &c. ; the yeast-plant, the 

 vinegar-plant, and other minute fungi con- 

 nected with fermentation ; the contagious 

 algas of the batrachia and fishes ; the muscar- 

 dine of the silkworm, are all well proved to 

 be communicable by the deposit of their 

 spores, or some part of their substance, upon 

 the external surfaces of the bodies of the 

 animals on which they grow, or by their intro- 

 duction into cavities opening on the exterior. 



Alltheinternal parasites, orEntozoa strictly 



* Ann. d. Sc. Nat. March, 1845, p. 182. 

 t See Article SEMEN. 



J Consult, especially, on the whole of this subject, 

 Dujardin's Hist. Nat. cles Infusoires, 1842. 



