SPONTANEOUS GENERATION, SO CALLED. 261 



derstood. As these organisms were studied more closely, 

 their multiplication by segmentation and by budding became 

 known, and these have since been described as processes of 

 generation peculiar to some of the lower orders of beings ; 

 but, at the same time, some writers revived the theory of 

 spontaneous generation, to account for the original appear- 

 ance of animalcules in water, and this idea has its advocates 

 at the present day. If, however, we follow out the history 

 of the spontaneous-generation theory, we find that the differ- 

 ent epochs have repeated themselves ; that the theory took 

 its origin from an ignorance of the mode of generation of 

 organisms quite high in the scale of being ; that the progress 

 of exact knowledge gradually restricted the theory to lower 

 and lower organisms, until, by this rigid process, it became 

 extinct, simply from want of material ; that its application 

 to entozoa was eliminated in the same way ; that it was re- 

 vived by the discovery of infusoria ; and that now its limits 

 have been restricted by positive advances in knowledge, it 

 being demonstrated, by Balbiani and others, that many varie- 

 ties of infusoria present the phenomena of sexual generation. 1 

 Of the advocates of spontaneous generation within a com- 

 paratively recent period, perhaps the most prominent has 

 been Pouchet ; a but modern researches have shown pretty 

 clearly that the infusoria produced in organic infusions are 

 due, in all probability, to the introduction of ova, or spores 

 floating in the air, which are developed when they meet with 

 proper conditions of heat and moisture. In numerous ex- 

 periments by different observers, which it is not necessary to 

 cite in detail, it appeared that, when organic infusions had 

 been exposed to a degree of heat sufficient to destroy germs, 

 and the introduction of new germs from the air was pre- 



1 BALBIANI, Reclierches sur les phenomenes sexuels des infusores. Journal, de 

 la physiologic, Paris, 1861, tome iv., pp. 102, 194, 431, 465. 



2 POUCHET, Theorie positive de Vovulation spontanee, etc., Paris, 1847. This 

 was followed by numerous other publications by Pouchet, and the views advanced 

 excited a most animated discussion in France and elsewhere, which continued for 

 several years. 



