72 Lectures on Bacteria. [ vm. 



kind should have some influence on the form of Bacteria is a 

 legitimate a priori assumption, and may be directly observed 

 from the facts stated on page 29. It is therefore highly 

 probable, though further distinct proof is required, that the 

 change of form of strongly pleomorphous Bacteria (see pp. 25-6) 

 is to a large extent determined by changes in the external 

 conditions of vegetation. 



In the natural course of things the processes of development 

 and decomposition of which we have been speaking, seldom if 

 ever go on their way purely and smoothly from beginning to 

 end. Many of the organisms in question are so numerous that 

 their germs find their way simultaneously or in rapid succession 

 into a nutrient solution or other decomposable substratum. In 

 that case they either develope simultaneously and the effects of 

 their decomposing action appear side by side ; or some find a 

 favourable substratum at first, but changing its character by their 

 vegetation, which is thereby impeded, they thus prepare a highly 

 favourable substratum for other forms ; in this way various de- 

 velopments and decompositions make their appearance, one 

 after another, in the same substratum. 



Examples of such combinations and successions of products 

 of fermentation and decomposition are found everywhere in the 

 natural course of things, and in matters connected with domestic 

 economy. There is less need for me to dwell on them here, 

 because many of them will have to be noticed in the succeeding 

 descriptions of the several species. 



VIII. 



Most important examples of Saprophytes. The nomen- 

 clature explained. Aquatic Saprophytes : Crenothrix, 

 Cladothrix, Beggiatoa; other aquatic forms. 



IN proceeding now to the special consideration of a few 

 saprophytic Bacteria, three remarks must first be made. First, 



