PEPTONIZING BACTERIA IN MILK 477 



granulose in their interior and spores. The latter can resist boiling 

 in water at 100 C. for one and one-half hours. These organisms 

 liquefy gelatin and coagulate milk. Grassberger claims that the non- 

 motile butyric acid bacilli are black-leg bacilli without pathogenic 

 properties. 



The Bacillus putrificus Bienenstock is a slender rod, 5 to 6 micra 

 long, with rounded ends. In gelatin, which is liquefied, it forms long 

 chains and pseudofilaments. The spores are formed at one end like 

 those of the tetanus bacillus and the sporulating organism has the 

 drum-stick appearance. This is best shown on agar or blood-serum 

 cultures. The spores can withstand heating at 80 C. for three 

 minutes, but they are killed in boiling water in five minutes. On 

 agar slants kept under anaerobic conditions the organism forms a 

 transparent veil and clouds the mass of the medium, also the water 

 of condensation. The organism may be obtained from hard cheese, 

 ground up fine and incubated with a nutrient bouillon, containing 

 0.5 c.c. lactic acid, kept under anaerobic conditions in the incubator 

 for ten to fourteen days. 



Other butyric-acid bacteria which have frequently been found in 

 milk are the Bacillus lactopropylbutyricus of Tissier and Gashing, 

 the Clostridium Pastorianum Winogradsky, and the Clostridium 

 Americanum of Pringsheim. The latter is not as strictly anaerobic 

 as the other species enumerated. This organism was found on 

 American potatoes. 



A bacterium frequently found in soft, strong-smelling cheese is 

 the Paraplectrum fetidum of Weigmann. It is a rod from 2.5 to 8 

 micra long, 0.6 micron thick; it forms spores in milk in two to three 

 days, and coagulates this fluid in forty-eight hours. The coagulation 

 is soon followed by a peptonizing liquefaction, with the formation 

 of a very fetid smell similar to that of limburger cheese. 



PEPTONIZING BACTERIA IN MILK. 



There are two groups of spore-forming, aerobic bacteria in par- 

 ticular which are very widespread in nature. They secrete enzymes 

 and almost invariably get into milk, in which they coagulate the casein 

 and subsequently liquefy it again. The coagulation, brought about 

 by a rennet enzyme, may be only very slightly marked, because the 

 peptonizing ferment is furnished by these bacteria so promptly and 

 evidently so abundantly that the peptonizing and liquefying action 

 greatly overshadows the coagulation. The bacteria of this type are 

 characterized by two representative species, the Bacillus subtilis, or 

 hay bacillus, and the Bacillus mesentericus vulgatus, or common 

 potato bacillus. They are present in the soil, in manure, on grains, 

 potatoes, hay, and straw, and in air and water. They are putrefying 

 organisms which, in connection with anaerobes with whom they live 

 in symbiotic community, are engaged in breaking up organic waste 



