178 TEXT-BOOK OF BACTERIOLOGY. 



A chemical change, very different from the one just described, is 

 brought about in milk by a special kind of bacterium, which has 

 also been carefully studied by Hueppe. 



Its rods are rather large, slender, and elegant, with rounded cor- 

 ners; they often occur in groups of two, but rarely form long 

 chains. They have a very lively power of locomotion, and at a 

 somewhat high temperature, say about 30° C, they produce spores 

 in the middle of the rods. These are gleaming oval-shaped bodies 

 which can be stained so as to distinguish them from the cell con- 

 tents. The non-sporulating cells take the anilin colors without 

 difficulty. 



On the glass plate at first appear small white points which 

 quickly gain the surface, liquefy the gelatin very energetically, and 

 soon make the observation of individual colonies impossible. Under 

 the microscope the deeper-lying colonies show j^ellow, lumpy masses, 

 When the liquefaction of the gelatin begins, the edge of the little 

 swarm of bacteria " unraA'els," and the colony soon has the ap- 

 pearance of a grayish-brown mass, evenly granulated. 



In the test-tube the gelatin is quickly. and extensively liquefied, 

 the liquefaction proceeding as a rule pretty generally through the 

 entire depth of the puncture, the gelatin being colored with a slight 

 yellow tinge. On the surface a thin whitish-gray skin, with deli- 

 cate wrinkles, is formed, but the chief mass of bacterial growth 

 remains suspended in the liquefied gelatin as a thick opaque cloud. 



On oblique agar the micro-organism grows as a light yellow^ 

 greasy coating. 



If a portion of pure culture is put into sterilized milk, a series of 

 chemical changes take place which are much favored by the tem- 

 perature of the incubator and free access of oxygen. 



First comes, without any perceptible change in the amphoteric 

 reaction of the milk, a general coagulation of the casein. It sinks 

 to the bottom in dense lumpy masses, and then begins at the end 

 of about eight days to decompose. The separated albumin is 

 changed into peptone and other products of decomposition, among 

 which ammonia holds a prominent place. At the same time the 

 milk becomes decidedly bitter to the taste. 



From this fact Hueppe drew the conclusion that the rod-cells 

 just described must be identical with the much-talked-of bacilli of 

 butyric fermentation, to which the same or similar influences have 

 been attributed and which are generally acknowledged to possess 

 such powers. 



There can, however, be no doubt that Hueppe's bacteria are not 

 identical with those exciters of butyric fermentation which have 



