AEROBIC LIFE AND ANAEROBIC LIFE 81 



time I thought it my duty to apply all my efforts to 

 dispelling the apparition of these little animals, from the 

 fear lest they nourished themselves on the vegetable 

 ferment which I supposed to be the butyric ferment, and 

 which I was trying to discover in the liquid medium that 

 I employed. But not able to find the origin of the bu- 

 tyric acid, I ended by being struck with the coincidence 

 which my analyses showed me to exist between this acid 

 and the Infusoria, and, reciprocally, between these 

 Infusoria and the production of this acid. We must 

 consider them the true butyric ferment." 



Thus Pasteur's surprise came from the intervention in 

 a fermentation of an organism which he considered to be 

 an animal because it was motile, while the non-motile 

 alcoholic and lactic ferments were considered as vege- 

 tables. We can to-day scarcely understand this aston- 

 ishment and these scruples. But from 1850 to 1860, the 

 old barriers established between the vegetable and animal 

 world had scarcely begun to fall. Although admitting 

 in his Recherches sur les zoospores des algues, which 

 appeared in 1851, that the green Infusoria and the Vol- 

 vocacea3 "present animal characters too pronounced and 

 too permanent for it to be possible to relegate them to 

 the vegetable kingdom," de Thuret insists, none the less, 

 on the difficulty of tracing an exact line of demarcation 

 between animals and the lower vegetables. "At this 

 time," writes my excellent confrere, M. Bornet, " motility 

 appeared to be so evidently an animal character that 

 Rabenhorst published, between 1849 and 1852, a collec- 

 tion of Diatoms and Desmids as Ein Beitrag zur Fauna 

 von Deutschland." Pasteur, who was not a naturalist, 

 was excusable for still holding this opinion in 1862, and 

 although astonished at his scruples, one must be pleased 

 with him for taking so much pains to efface them from 

 his mind. He did not suspect then that this discovery 



