GROWTH OF BACTERIA IN NORMAL MILK. 67 



results shown by the previous tables. It will be noticed, how- 

 ever, that there was an exceptionally large number of the 

 species No. 220, which was the .same organism that appeared 

 in the last series of experiments. This organism was found 

 in the first two tests in large numbers, but in the later tests 

 did not appear. It is possible that the presence of this new 

 organism was a.ssociated with the fact that in this experiment, 

 as in the last, the animals were fed from a different lot of hay, 

 which might very likel}^ have contained some species of organ- 

 isms differing from those previously found, which would explain 

 the appearance of this No. 220 in such large numbers. 



SAMPLE KEPT AT 1 3 DEGREES. 



1. There was noticed, as before, in the milk kept at 13°, 

 no increase in total number of bacteria for forty hours; indeed, 

 the sample at the end of forty hours contained not quite half 

 as many as the fresh sample of milk. In the next twelve 

 hours there was, as in the previous experiments, an increase 

 in total number of bacteria. It will be seen further that this 

 increase that occurred between forty and fifty-two hours was 

 due chiefly to the development of the Streptococais and lique- 

 fying organisms. 



2. The most striking difference between this and the last 

 experiment is seen in the growth of the Sarcina. Whereas in 

 the experiment of January 24th this species was present in the 

 first forty hours in large numbers, over 50 per cent, of the 

 whole, in this sample there were present at the outset only .7 

 of a per cent.^ — about 100 per cubic centimeter — and in the 

 subsequent tests the presence of this species was doubtful, 

 until the last one when they increased in numbers slightly. 



3. The liquefiers remained throughout this series of plates in 

 about the same relative proportions, varying somewhat in differ- 

 ent tests and increasing considerably in the last twelve hours. 



4. The acid organism No. 220, present in the first plates, 

 disappeared entirely from the later tests in this experiment, 

 whereas in the last experiment this species continued to be 

 present up to the end of forty hours. 



Experiment No. ij. February ^. — This experiment is a 

 repetition of Experiments Nos. 11 and 12. The results are 

 shown in Tables 33-36 following: 



