110 BACTERIA IN MILK 



an acid reaction, but it never shows the predominance of Str. 

 lacticus found at 20 C. 



(8) From our experiments there seems to be no difference 

 between the effect of 10 and 1 upon the bacteria, except upon 

 the rapidity of growth. 1 C. very markedly checks the growth 

 of bacteria; but, later they grow in large numbers. As at 

 10 C., the lactic bacteria fail to outgrow the other species, so 

 that all types develop abundantly. A few species appear to be 

 particularly well adapted to this low temperature and are espe- 

 cially abundant at the end of the experiment. 



(9) The curdling point appears to be quite independent of 

 the number of bacteria present. In one sample at 37 C., the 

 milk curdled with only 8,000,000 organisms per c.cm. while 

 in others there have been found 4,000,000,000 per c.cm. without 

 any curdling. These differences are apparently due to the 

 development of enzymes, and partly to the products of some 

 species neutralising the action of others. The amount of acid 

 present at the time of ordinary acid curdling does not widely 

 vary. 



(10) Milk is not necessarily wholesome because it is sweet, 

 especially if it has been kept at low temperatures. At the 

 temperature of an ice box milk may remain sweet for a long 

 time and yet contain enormous numbers of bacteria, among 

 which are species more likely to be unwholesome than those 

 that develop at 20 C. 



Although these results show that temperature exerts a 

 selective action on the bacterial flora it must not be forgotten 

 that this may be wholly or partially negatived by a predominance 

 of any particular species in the original milk. For example, 

 milk produced under good conditions and containing less than 

 10,000 bacteria per c.cm. will very rarely show a predominance 

 of coliform organisms even when incubated at 37 C. The 

 curd produced by this class of milk is almost invariably of the 

 smooth acid type produced by Str. lacticus and seldom gives 

 the gas-blown curd typical of the B. coli group. An examina- 

 tion of the type of curd produced on incubation at 37 C. has 



