THE LACTIC BACTERIA. 



lactic species shows variations under different conditions, 

 and the descriptions of the same organism do not always 

 agree because of different conditions and different methods 

 of study. As the result of these facts it has been quite im- 

 possible until recently to state what .were and what were not 

 the primary lactic bacteria. At the present time, however, 

 enough work has been done to enable us to see some order 

 in this chaos and to reduce the facts to an intelligible system. 



Nearly all of the lactic bacteria described are short, oval 

 rods or cocci, resembling each other closely in size and 

 shape. Practically all of them agree in failing to develop 

 spores and in being consequently killed by moderate heat. 

 Among the large list of lactic species described are many 

 that are purely incidental, found only occasionally in milk 

 and in small numbers, but present so rarely and in such 

 small numbers that they have little or nothing to do with 

 ordinary dairy problems. If we omit these incidental spe- 

 cies from our list the rest may be 

 readily grouped into a few simple 

 types. 



i. A Facultative Anaerobic Type. 

 The first type consists of bacteria 

 which do not flourish in the presence 

 of oxygen, growing better where the 

 amount of oxygen is slight. They 

 are .what is known as facultative 

 anaerobes. The bacteria included 

 under this head have the following 

 chief characters (43) : They are 

 short rods, showing considerable 

 variation in length from forms so 

 short as to be practically almost 

 spherical to others that are twice as long as broad. The 

 same species show these variations and have been some- 

 times described as micro cocci and sometimes as bacilli or 



FIG. 12. 



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o o 



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Lactic Bacteria of the common 

 type showing variations in 

 shape, a and b are the same 

 species, c, d, and e are three 

 forms of a second species. 



