THE BEGINNINGS OP LIFE. 325 



Although the movements of Bacteria are, therefore, 

 frequently of so extensive a nature as to render it not 

 at all doubtful whether the organisms which display 

 them are living, it becomes obvious that we ought not 

 to rely too strongly upon the mere vibratory character 

 of their movements, as evidence of the death of Bacteria. 

 In the experiments which I am about to relate, we shall 

 be able to pronounce that the Bacteria are living or dead, 

 by reference to the continuance or cessation of a much 

 more essentially vital characteristic. If Bacteria fail 

 to multiply in a suitable fluid, and under suitable con- 

 ditions, we have the best proof that can be obtained 

 of their death. 



Having made many experiments with solutions of 

 ammonic tartrate and sodic phosphate, I have almost 

 invariably observed that such solutions when exposed 

 to the air without having been boiled become turbid 

 in the course of a few days owing to the presence of 

 myriads of Bacteria and Vibriones^ with some Torul*. 

 These organisms seem to appear and multiply in such 

 a solution almost as readily as they do in an organic 

 infusion. On the other hand, having frequently boiled 

 similar solutions, and closed the flasks during ebullition, 

 I have invariably found, on subsequent examination 

 of these fluids, that whatever else may have been met 

 with, Bacteria and Vlbriones were always absent. The 

 difference was most notable, and it seemed only intel- 

 ligible on the supposition that any living 'Bacteria or 

 dead ferments which may have pre-existed in the 



