GROWTH OF BACTERIA IN NORMAI. MILK. 75 



6. The liquefiers failed to develop in this sample, being 

 present only in small nnmbers at the end. 



7. The miscellaneous species, which were numerous, con- 

 tinued to remain through the whole experiment in about equal 

 numbers, nearly every plate made showing most of these 

 species present in small numbers and in small percentage. In 

 other words, in this experiment the development of the lactic 

 organisms did not, as usual, result in the decrease of the mis- 

 cellaneous species. 



8. From these facts it is seen that the increase in numbers 

 occurring from the thirty-eighth to the fiftieth hour was due 

 to the excessive growth of B. acidi ladici II. , which resulted 

 in a marked relative decline in percentage of all the other 

 species present. 



SUMMARY OF THE EFFECT OF PRESERVING THE MILK AT 

 13 DEGREES. 



1. A temperature of 13° has an unexpected effect upon the 

 total number of bacteria, as can be seen from the results given 

 in the foregoing tables. For a period of from thirty-six to thirty- 

 eight hours the bacteria fail to grow at all, and may at this 

 time be actually less in numbers than at the outset. This 

 phenomenon is similar to that which occurs in milk at 70° for 

 six hours, and may perhaps be regarded as a continuation of 

 the so-called "germicidal action" of the milk. After about 

 forty-eight hours the number of bacteria begins to increase, 

 but even at fifty hours, the limit of our experiments, the num- 

 ber is very small. It will be seen that at fifty hours the number 

 of bacteria in milk kept at 13° is no more than is present at 

 eighteen hours in milk which is preserved at 20°. 



2. After about the fortieth hour the growth of bacteria 

 begins, but it is seen that some of the species of bacteria are 

 different from those which develop in milk which is kept 

 at 20°. 



3. The action of this temperature is apparently to check 

 very decidedly the growth of B. acidi ladici, which, although 

 not killed, remains even to the end of the experiments, as a 

 rule, in small numbers, and is hardly more abundant at the 

 end of the experiment than at the beginning. There is com- 

 monly a slight increase in numbers in the last twelve hours. 



