180 TEXT-BOOK OF BACTERIOLOGY. 



substances when kept damp (for instance, in the case of the wet- 

 rot of potatoes), and even to separate cellulose into its component 

 parts. 



The manifold action of the butyric-acid bacilli occurs at 40 C., 

 and only with restricted admission of oxygen. 



It hardly needs to be added that this species of bacterium has an 

 immensely wide diffusion in nature. It is worthy of mention that 

 traces of its existence have been found as far back as the coal 

 period at least van Tieghem has been able to recognize bacteria 

 in thin sections of the roots of conifera from that age, which from 

 their form he thought himself justified in pronouncing to be cells of 

 Clostridium butyricum. 



More exact investigations with regard to this so important spe- 

 cies are certainly very desirable. Such investigations will, perhaps, 

 show that just as the Bacillus acidi lactici is in most cases the ex- 

 citer of lactic fermentation, so also Clostridium butyricum generally 

 causes the formation of butyric acid, while here also quite a num- 

 ber of other micro-organisms possess the same power. 



BACILLUS CYANOGENUS. 



We have already seen that a special disease of cows was for a 

 long time supposed to be the cause of that peculiar red color in the 

 milk which is produced under some circumstances by Micrococcus 

 prodigiosus, as also by Sarcina rosea, and other micro-organisms. 

 A similar cause was formerly supposed to bring about that blue- 

 ness of the milk which, especially in the summer months, is no 

 rarity in our North German dairies. Bad food, damp meadows, 

 etc., were often blamed as the more or less direct cause of its ap- 

 pearance. 



The investigations of Fuchs and Neelsen proved, however, that 

 this discoloration of the milk is due to the action of bacteria, and 

 indeed of one definite species, which has therefore been called the 

 blue-milk bacillus (Bac. cyanogenus). 



They are rather slender rods, about twice or three times as long 

 as they are broad, with slightly-rounded corners, which are often 

 united in twos, but are scarcely ever found in more numerous 

 groups. They have an extremely lively spontaneous movement, 

 which continues for hours in a hanging drop. The formation of 

 spores has been observed as early as the third day in milk, in gela- 

 tin, and still more favorably in a slimy decoction of marsh-mallow 

 roots. Small, gleaming bodies are seen to arise at one end of the 

 rod. 



