GROWTH OF BACTERIA IN NORMAL MILK. 45 



falling at the end to .4 of one per cent. The actual numbers 

 were, however, large in the last experiment, showing that the 

 small percentage of these organisms was due to the large num- 

 bers of B. acidi lacHci. 



A fourth point of difference was in the liquefiers. Whereas 

 in the first experiment the number of liquefiers was 10 per 

 cent, at the outset and rose to 65 per cent. , falling at the end 

 to 39 per cent., the number in the second experiment was in 

 no case over 14 per cent, and at the end had fallen to .6 of one 

 per cent. 



There are other minor differences that may be made out 

 from the stud}^ of the tables but these four represent the more 

 important. It is not improbable that it was the great develop- 

 ment of liquefiers which modified the development of the other 

 species and that the difference between these two samples is to 

 be explained by the fact that for some quite inexplicable rea- 

 son the liquefiers developed rapidly in the first sample and 

 failed to develop in the second sample. 



When these two tables are compared with those of experi- 

 ments of earlier dates. Tables i-io, there are found to be no very 

 considerable differences. There is in each case an increase of 

 acid organisms, a decrease in the miscellaneous species and a 

 general increase in liquefiers. It will be noticed, however, 

 that the experiment of January 17 was in some respects quite 

 anomalous. The number of acid bacteria at the end of twenty- 

 seven hours is much greater than in an}^ previous experiment 

 described. The total number of bacteria is very large, 43,000,- 

 000, and of these over 90 per cent, are lactic bacteria. The 

 result of this is, as seen by Tables 12 and 14, that most of the 

 other types of micro-organisms have become reduced in pro- 

 portion or have quite disappeared. The results obtained in 

 this experiment are quite similar to those which have been 

 given in a previous report-'^ upon the development of bacteria 

 in the late stages of cream ripening, where, as has been shown, 

 the excessive development of lactic bacteria forces all other 

 species to the background and eventually appears to destroy 

 them. This sample of milk at the age of twenty-seven hours 

 is, so far as concerns its type of bacteria, quite similar to the 

 samples of milk and cream of a very much older age which are 

 described elsewhere, f 



* Storrs Elxpt. Sta. Rept., 1900, pp. 13-33. t Loc. Cit. 



