673 NATURE OF REPRODUCTION. 



Schultze 1 performed similar experiments, with the additional advan- 

 tage of admitting to the organic infusion fresh air purified from germs. 

 He placed his infusion in a glass flask, the stopper of which was pro- 

 vided with two narrow tubes, bent at right angles. When the infusion 

 had been thoroughly boiled, and all the air contained in the flask ex- 

 pelled, he fastened to each of the projecting tubes a series of bulbs 

 containing on the one side sulphuric acid, and on the other a solution 

 of potassium hydrate ; so that the air which re-entered the flask while 

 it was cooling must pass through these fluids, and thus be cleansed of 

 all living organic matter. The apparatus was then kept in a warm 

 place for two months, the air being renewed daily by suction through 

 the tubes, without any infusoria being detected in its contents. But 

 they showed themselves in great abundance after it had been taken 

 apart, and the infusion exposed for a few days directly to the atmo- 

 sphere. 



Pasteur' 2 found that if a flask containing an organic liquid were boiled 

 upon a high mountain, where the air is of unusual purity, allowed to 

 fill itself with this air while cooling, and then hermetically sealed, it 

 would often remain free from infusorial growth. He kept several such 

 flasks, boiled and filled with air upon the Montanvert in Switzerland, 

 for four years, without the liquids which they contained undergoing any 

 perceptible change. But on making, at the end of that time, a minute 

 opening in the neck of one of these flasks, it exhibited after three days 

 a perceptible growth of cryptogamic vegetation. 



These results did not absolutely exclude the possibility of spontane- 

 ous generation, which was still maintained by Pouchet and a number 

 of other observers ; but they indicated in a very decisive manner that 

 the atmosphere might contain the inactive germs of infusoria, which 

 were capable of being developed on meeting with a suitable organic 

 infusion. 



But in the mean time the study of the infusoria themselves had been 

 going on independently of the question of spontaneous generation, and 

 this alone has been sufficient to demonstrate that they are reproduced 

 in the usual way, like other animal species, by means of fertilized eggs 

 and embryonic development. 



The apparent confusion and variability in form of the infusoria, at 

 the time of their first discovery, depended only upon their great num- 

 bers and upon the want of sufficient knowledge in regard to them. Sub- 

 sequent observation has shown that their organization is as definite as 

 that of other classes of the animal kingdom ; and they have now been 

 arranged, by the labors of Claparede and Lachmann, 3 Stein, 4 and Bal- 

 biani, 5 into orders, families, genera, and species, which may be recog- 



Poggendorf s Annalen, 1836. Band xxxix. p. 487. 



Comptes Rendus de I'Academie des Sciences. Paris, Fevrier 20, 1865. 



Etudes sur les Infusoires et les Rhizopodes. Geneve, 1856-1861. 



Organismus der Infusionsthiere. Leipzig, 1859. 



Journal de la Physiologic de PHomme et des Animaux. Paris, 1861. 



