6o BACTERIA. 



the question of Spontaneous Generation or generatio 

 lequivoca ; and to the disciples of that school every acknow- 

 ledgment must be madfe and due credit assigned for the 

 attitude of scepticism and free ingenious and honest criticism 

 which they passed concerning half-formed and inadequately- 

 supported theories and imperfectly-conducted experiments, 

 for to their eiforts is certainly due the fact that the 

 experiments of their opponents became more and more 

 perfect, and if to-day we have perfect methods of sterilization 

 and of making pure cultivations, it is because nothing was 

 taken for granted, and because able men on both sides of the 

 controversy were ranged against one another to fight the 

 matter to the death. 



Whilst this battle over the origin and development of these micro- 

 organisms was going on, intermittent attempts were made to improve on 

 the classification that had been drawn up by Miiller, but it was only as 

 the optician supplied observers with better microscopic apparatus that 

 any further advances could be made. Ehrenberg, however, took up the 

 question and divided the Monad family into rounded and rod-shaped forms ; 

 these latter — Vibriones — he described as undergoing transverse division, 

 as they increased in length. These he sub-divided into Bacteria, or short, 

 straight, inflexible organisms ; Vibriones, longer and more flexible ; Spirilla, 

 or inflexible spiral forms ; and the Spirochsetse, or the flexible spiral organisms. 

 If to this classification we add the Cocci or rounded forms, we have prac- 

 tically a rude model of that adopted by authors at the present time. In his 

 vibriones he had six varieties, of which lineola, rugula, and bacillus, had 

 already been described by Miiller, but subtilis, tremulans, and prolifer, 

 were new. In consequence, however, of the want of marks of characteri- 

 zation, Ehrenberg himself was very doubtful as to the propriety of his 

 system of division or nomenclature. His spirillum comprises three forms, 

 the old vibrio undula of Miiller, the ordinary spirillum, and a new kind of 

 spirillum (Tenue). These three differed from one another only as regards 

 length and thickness, the Vibrio undula having only from one to one and a 

 half spiral windings, the others being merely longer or thicker. His genus, 

 Spirochffita, contained a single form only, the Spirochseta plicatilis, an 

 organism of great length, but of very small diameter. 



In consequence of the active snake-like and rotary move- 

 ment of these organisms, Ehrenberg was fully convinced 

 that he had to deal with animals, and this opinion was uni- 

 versally accepted down to the time when Davaine gave his 

 opinion that bacteria must be classified as really belonging 

 to the vegetable kingdom. 



In 1840 colour characteristics were brought into play as a 

 means oiF distinguishing certain organisms, and we find that 

 Fuchs and Ehrenberg describe Vibrio cyanogenus and Bacil- 



