BACTERIA 43 



number of nearly related obligate anaerobic bacteria to be described 

 in connection with the putrefactive process. As all the non- 

 sporing bacteria in a liquid can be killed by heating for a few 

 minutes at 90 C., the sporing organisms may readily be isolated by 

 this means. If the liquid is rich in butyric acid bacteria, a small 

 quantity may be inoculated after heating, into a tube containing 

 a deep layer of sugar agar, but if only a few of these organisms are 

 present their number must be increased by adding the heated 

 liquid to sterile milk which all but fills a bottle securely closed by 

 a spring stopper ; the fermentation should not be allowed to 

 proceed too far before the bottle is opened, or the pressure of the 

 accumulated gases may easily cause a burst. The butyric acid 

 bacteria ferment most sugars (not mannitol), and are said to 

 be able to ferment starch. Butyric acid is the chief product 

 formed in milk. They occur principally in soil, manure and 

 flour. 



According to Grassberger and Schattenfroh 1 , distinction is to be 

 made between the motile and the non-motile forms, Bacillus 

 butyricus mobilis and B. b. immobilis. The former is peritrich, 

 and readily forms spores which are killed after only three minutes' 

 boiling ; it does not ferment calcium lactate. It is responsible for 

 the large amounts of butyric acid found in certain sour milk 

 cheeses 2 . The latter is somewhat larger and forms spores less 

 readily, but on the other hand the spores are decidedly more 

 resistant to heat, for they will survive one and a half hours' boiling. 

 According to Barthel 3 , it is far more common in milk than the 

 motile form, which accounts for its regular occurrence in the human 

 and animal intestines. As a gas-producing organism, it may give 

 rise to the formation of cavities in cheese. It may sometimes be 

 pathogenic, and is supposed by some to be merely a degene- 

 rated variety of the organism of the cattle disease, blackleg or 

 quarter evil (Bacillus Chauvoei), which is normally peritrich and 

 attacks proteins. The butyric acid bacteria grow well at 16 to 

 40 C. 



While the butyric acid bacteria do not attack cellulose, a number 

 of closely related Plectridium forms carry out a cellulose fermenta- 

 tion which is of prime importance in the digestive process of herbi- 

 vora and in soil formation. Other allied forms ferment the 

 pectins which cement together the vegetable cells, and come to 

 play an important part in the retting of flax and hemp. 



1 "Archiv. f. Hygieine," XXXVII., XLII. and XLVIII. 



2 Freudenreich and Orla- Jensen, " Landwirtschaftliches Jahrbuch der 

 Schweiz," 1905, p. 312. 



3 " Obligat anaerobe Bakterien in Milch und Molkereiprodukten " 

 ("Centralblatt 1 Bacteriologie/' 2 Abt., 1910, Bd. XXVI. , p. 1). 



