152 UNIVERSITY OF COLORADO STUDIES 



Ehrlenmeyer flasks of 300 c.c. capacity. In seven examinations one 

 of these flasks was left at 17 degrees C. In the remaining fourteen 

 one was kept on ice and one at room temperature. Plate cultures 

 were made by placing in Petri dishes definite quantities of the milk 

 to be examined, and then there was poured into the Petri dishes 

 melted nutrient agar and this mixed thoroughly with the milk or 

 milk dilutions. The first plates and reaction determinations could 

 be made from either of the flasks. All later work was carried out 

 complete from each flask. In every case the reaction was deter- 

 mined to phenolphthalein. 



In six of the samples only one set of plates was made using dilu- 

 tions of 1/ 10 c.c. to I / 1000 c.c, according to the age of the milk. All 

 of these plates were incubated at 18 to 20 degrees C, which is consid- 

 ered the average room temperature. Following this first set, plates 

 were made the following evening and then morning and evening until 

 the milk loppered, in each subsequent plating increasing the dilution^ 

 by ten to one hundred times. These plates were incubated in the 

 same manner. After twenty-four to forty-eight hours, according to 

 the rapidity of the growth, each plate was coimted and an average 

 taken. 



In the last ten samples examined, plates were made from the flask 

 at room temperature and from that in the ice-box. The reaction 

 was taken from each. Also determinations for butter fat and for the 

 presence of formaldehyde and boric acid were made in each case. 

 By means of this method of examination not only the number of 

 germs in the milk when first received was determined, but also, to 

 some extent, the kind of germs and the time limit these germs place on 

 each milk for its desirability as food. For instance, we find two 

 milks when received (five hours after milking) to have approximately 

 the same number of germs. Later, one is foimd to have 1,617,200 

 germs in one cubic centimeter, while the other, two hours later than 

 this, has 10,405,500 germs per cubic centimeter. The reaction of the 

 first milk did not change from that when received, namely 10°. Un- 



' This work was done under my direction by Mr. Chaxles F. Poe. The data obtained^will be used by 

 Mr. Poe in a more exhaustive report to appear later as a thesis for a Master's degree. 



