BACTERIA 



29 



As bacteria may lose the power to form spores, the distinction 

 between the bacterium and the bacillus groups is not sharp. 

 The distinctions between the micrococci and the sarcinae, 

 and between the vibrios and other monotrich rod forms, are 

 still more ill-defined. On the whole, the above system of 

 classification, due to Lehmann and Neumann, is unsatisfactory, 

 as it groups together organisms which have but little in 

 common and separates others which should be grouped 

 together. It is only mentioned here as being that which is 



As far as the true lactic acid bacteria are 

 to use generic terms of more essential 



may be classified the Sulphur 

 Bacteria and the Ray Fungi. Sulphur 



FIG. 32. Aetinomyces boris. (After 

 Bostrom.) X 1,000. 



most commonly used, 

 concerned, I propose 

 significance. 



Together with the bacteria 

 Bacteria, the Thread 

 bacteria are always present 

 where hydrogen sulphide is pro- 

 duced, for example in rotting 

 seaweed, where they transform 

 the poisonous gas into sulphates 

 necessary for plant growth. 

 Colourless and red species are 

 known in forms of almost end- 

 less variety. The thread bac- 

 teria, like the sulphur bacteria, 

 are typical water organisms ; 

 they are found attached to solid 

 objects, and their outer cell walls 

 form sheaths in which may be accumulated large amounts of iron. 

 They may cause stoppages in water pipes, and contribute towards 

 the formation of bog-ore. The ray fungi, or Actinomycetes, may 

 be regarded as being intermediate between the bacteria and the 

 moulds, especially the Mycomycetse (Mucorinse) ; on the one hand 

 their cells are as slender as those of the bacteria, on the other 

 hand they ramify and form oidia by constriction. They are of 

 very common occurrence in soil, contributing to its characteristic 

 smell. They may develop in butter, in which they produce a 

 similar smell 1 . One variety, Aetinomyces bovis (Fig. 32), is the 

 cause of actinomycosis in cattle. The organisms of diphtheria, 

 and especially those of tuberculosis, are closely related to this 

 group. 



The Spirilla are also typical water bacteria, being difficult to 

 cultivate artificially. As representing the vibrios, only the well- 

 known cholera vibrio need be mentioned (Fig. 30). In dairy 



1 Orla Jensen, " Centralblatt fur Bacteriologie," 2 Abt., 1902, Bd. VIII., 

 p. 250. 



