54 BACTERIA. 



With a well-defined plan he set himself to systematize and 

 arrange the various organisms that had been described by 

 previous observers commencing with Leeuwenhoek and 

 ending with Spallanzani. 



When the nature of the optical apparatus Muller had at his disposal is 

 taken into consideration, it must be acknowledged that he succeeded in a 

 most marvellous manner in classifying, on the Linnaean system, the minute 

 organisms with which he had to deal. Under the head of Infusoria 

 he divided them into two classes those that could be seen with the 

 naked eye, and those that were invisible except with the assistance 

 of a microscope. The latter class he again divided into Membranacea, 

 or those forming thin surface membranes, and Crassuiscula, or those 

 forming thick membranes ; these latter, including Monas, Proteus, Volvox, 

 Enchelys, and Vibrio, representing, he maintained, the lowest forms of 

 animal life. Of Monas he described no fewer than ten species, and of 

 Vibrio he was able to distinguish, by utilizing the characters of form, 

 motion, nidus or cultivation medium, and other biological features, thirty- 

 one species. Relying, however, principally on the form of the organism, 

 he described rounded and slightly oval forms, shorter and longer rods, 

 rounded and truncated cork-screw-shaped and snake-like organisms, 

 undulating but not spiral in their movements, and also long threads or 

 bacilli. 



Although he did not fully recognize the importance of his 

 observation he described in certain organisms little shining 

 points, arranged in series at regular intervals, especially in 

 the rod-shaped forms, points which we must now conclude 

 were spores. It is certainly not remarkable that he should 

 never have understood the full significance of these spores, 

 as even ninety years later, with all the additional light 

 that had then been thrown on the subject, these bodies were 

 still not properly understood. Later observers laid stress on 

 the rapidity of movement of the vibriones or lineolae, which 

 were gradually separated from the other forms of lower 

 organisms. The vibriones then described, including lineola, 

 rugula, bacillus, and spirillum, correspond more or less per- 

 fectly with our bacteria of the present day. 



Many advances were made after Miiller's work was com- 

 pleted as regards the morphology of these organisms, but 

 the question .as to whence these minute forms came still 

 remained unanswered. Whether they were the result of 

 spontaneous generation, or were the progeny of pre- 

 existing forms, was the question which for over a century 

 occupied the minds of those engaged in scientific research 

 and speculation. Some observers, prominent amongst whom 



