observers that each worm proceeded, though often by 

 devious ways, from a similar pre-existing organism ; found 

 a tower of strength in the bacteria, a position fortified 

 by a series of careful, conscientious, and delicate ex- 

 periments by Bastian and Pouchet. The result of that 

 contest is known to all. The errors in manipulation 

 and interpretation upon which the proof of sponta- 

 neous generation rested were detected, and a series of 

 hitherto unassailable experiments by Pasteur, Tyndall, 

 Traube, and Brefeld compelled the admission that bac- 

 teria, like the intestinal worms and the maggots, and 

 all other living things, illustrate the dogma, " oinne vi- 

 vum ex ovo ! " Yet this phantasy of spontaneous gene- 

 ration seems a spook which can never be exorcised from 

 man's imagination. Quite recently Arndt has deduced 

 from experiments, to which I shall presently refer, a con- 

 clusion which may be regarded as modified spontaneous 

 generation ; namely, that certain elements of animal- 

 cells can, under favoring conditions, continue to exist and 

 develop into bacteria after the death of the cells of which 

 they were previously constituent molecules. Yet the evi- 

 dence adduced does not as yet warrant any hesitation in 

 accepting the current doctrine that bacteria, like all other 

 organisms, proceed from pre-existent similar beings. 



In order to discuss intelligibly the individual bacteria, 

 we must agree upon a classification. The nomenclature 

 has given rise to much discussion and more confusion. 

 At first each investigator christened, after his own fancy, 

 every new variety. The French school, first in the 

 field by virtue of Pasteur's work on fermentation, em- 

 ployed, very loosely, the terms vibrios, monads, toru- 

 lacese, etc. Natural selection has proven Cohn's classi- 

 fication the fittest to survive, which is quite natural, 

 since the greater part of our exact knowledge of this sub- 

 ject is due to this distinguished botanist and his pupils. 

 Cohn's original classification permits and will doubtless 

 need amendments ; in fact, he has already proposed 

 some essential modifications based chiefly upon the form 

 and mode of association of the individual cells. I shall 



