478 PEPTONIZING BACTERIA IN MILK 



material into very simple chemical compounds. They get into milk 

 during milking, with the dust from hay and straw, and they are 

 undoubtedly also found on the skin of the cow's udder. They are 

 not numerous in cow's feces, hence they do not indicate contamination 

 by manure. 



Bacillus Subtilis. The Bacillus subtilis can be easily obtained by 

 making an infusion of hay, boiling it for one hour, and incubating it 

 at 37 C. The boiling destroys the vegetative forms of all kinds of 

 bacteria, but does not affect the spores of the Bacillus subtilis. The 

 latter is a rod 4 to 5 micra long and 0.8 to 1.2 micron thick; some- 

 times very short rods are seen, also long chains and pseudofilaments. 

 The bacillus is motile and possesses eight to twelve flagella, arranged 

 around the body of the organism. The spores are formed in the centre, 

 sometimes more toward one end of the bacillus. When germinating 

 they rupture the spore membrane in the equatorial plane, not at 

 either end. The elongating young bacillus sometimes carries the 

 empty spore membrane along, attached to it like a cap. On gelatin 

 small, white, punctate colonies are formed, which later become darker, 

 granular and brownish, and send out hair-like processes into the 

 culture soil. The colonies rapidly liquefy gelatin. On gelatin stick 

 cultures rapid liquefaction occurs along the whole line of the stick. 

 On agar slants a heavy, corrugated growth is formed. Blood serum 

 is likewise liquefied. The bacillus grows well and abundantly on 

 potatoes. As already stated, it peptonizes milk very rapidly, but its 

 growth in milk is prevented as soon as lactic-acid bacteria have 

 formed a small amount of lactic acid. According to Lafar the presence 

 of 0.1 per cent, of lactic acid prevents the development of the Bacillus 

 subtilis. It is a strictly aerobic organism, and requires for its best 

 growth an abundant supply of oxygen. The organism is Gram 

 positive. 



Bacillus Mesentericus Vulgatus. The Bacillus mesentericus vulgatus 

 is a widely prevalent saprophyte. It is the most common of the group 

 of potato bacilli and is somewhat smaller than the Bacillus subtilis. 

 It is motile and possesses numerous flagella, which generally are found 

 on one side of the body only. The spores are elliptical and large. 

 On gelatin the growth closely resembles that of the Bacillus subtilis 

 and liquefies it energetically. In milk coagulation is more marked 

 than in the case of the subtilis, but subsequent liquefaction is also 

 soon accomplished. On potatoes the growth is very abundant and 

 forms a thick, corrugated layer. The organism occurs in several 

 varieties, such as the Bacillus mesentericus fuscus, which forms a 

 grayish-brown pigment, and the Bacillus mesentericus ruber, which 

 forms a reddish-yellow pigment. The Bacillus liodermes, or rubber 

 bacillus of Loeffler, which also belongs to the same group, forms 

 a rubber-like growth on potatoes. 



The common root bacillus, Bacillus mycoides, so called on account 

 of its rizoid cultures on gelatin, is also frequently found in milk. 



