174 -CLASSIFICATION OF THE MICRO-ORGANISMS. 



DIVISION 3. SPIRILLA. 



Morphological The typical forms are spirally twisted threads, which 

 ) C h-ma 0f P r duce new spirals by fission, and which are for the 

 most part mobile and often united in swarms. As 

 to the existence of a cycle of forms in the spirilla 

 there is very little known, but they seem to have a 

 special tendency to the formation of involution forms. 

 In the case of some spirilla it can be distinctly seen 

 that the spirals are composed of short, curved rods ; 

 under certain circumstances these rods form the pro- 

 minent vegetative form, while under other conditions 

 they become fused together, and spiral threads are 

 developed. A precise differentiation of these rod-shaped 

 spiral elements from true bacilli, which often show 

 a slight curvature in microscopical preparations, i^ 

 frequently very difficult ; and it will probably be im- 

 possible, as our knowledge increases and transitional 

 forms are discovered, to uphold the genus spirillum as 

 an independent division. In the meantime, however, it 

 appears desirable on practical grounds to group together 

 m the genus spirillum those curved bacilli in which a 

 development of spiral threads and a multiplication in that 

 vegetative form is observed. 



DIVISION 4. FISSION FUNGI WITH VARIABLE VEGETATIVE 

 FORMS. 



Characters of The aquatic fungi studied by Zopf (formerly described 

 as fission algae) cladothrix, beggiatoa, crenothrix can- 

 not be included in any of the foregoing divisions. In 



forms. these fungi, according to Zopf, a manifold cycle of 



forms occurs, so that one and the same fungus may 

 appear in micrococcal, bacillar, and spirillar vegetative 

 forms. It is possible that in course of time other 

 bacteria may become known in which an equally exten- 

 sive series of forms occur. The species which can at the 

 present time be included with certainty in this group 

 are comparatively easily recognised and distinguished 



