CLARIFICATION OF MILK. 217 



increase in the bacterial content after clarification over the same milk 

 unclarified. 



3. The slime sediment reveals a deposit of bacteria which of com-se 

 must come out of the milk undergoing clarification (see page 190). 



There seems to be a tendency, which is not universal because the milk 

 from different cows varies so, for milk at the time of milking (70 per cent, 

 of the cases) to undergo a reduction in the number of bacteria after clari- 

 fication as revealed by plating, while milk which stands increases in its 

 number of bacteria after clarification in direct proportion to the time that 

 it is permitted to stand before clarification. 



This would indicate that fresh certified milk is freer from colonies and 

 has a greater number of single organisms, and these single bacteria are 

 thrown out with the slime (see "Slime," page 195), in some cases to a 

 considerable extent. In certain instances, however, colonies have formed 

 and are disrupted, thus increasing the bacterial content of certified clari- 

 fied milk (30 per cent, of the cases). 



The commercial milk appears to admit of so much colonizing with the 

 subsequent disruption by the clarifier that a high percentage (85 to 90 

 per cent.) of samples will give an increased number of bacteria after clari- 

 fication. Since a large number of bacteria is found in the slitne, and 

 there is little opportunity for multiplication during the process of clari- 

 fication, the increase in the number of bacteria is only apparent and not 

 real. 



Thus far we are substantially in accord with the report of the Biochem- 

 ical Laboratory of Boston, Hammer and Bahlman. Assuming that micro- 

 organisms have no time to multiply, it follows that although a count- 

 increase is evidenced by the plating method, the number is actually 

 reduced by those appearing in the slime. 



Serial Counts of Micro-organisms in Clarified and Unclarified Milk over a 



Period of Time. 

 Together with the single bacterial counts of milk before and after clarifi- 

 cation should be considered two-hour counts of milk, certified and market, 

 unclarified and clarified, extending over seventy-two hours. This study 

 will give a more precise knowledge of the effect of clarification upon the 

 germ-content of milk in spite of the errors creeping in from colonization 

 and plating. It will be seen at once that the graphs depict a situation not 

 revealed by the single count before and after clarification, and they corre- 

 spond more closely with actual experience. This taken together with, 

 other factors, as the character of fermentation resulting from clarification 

 (see page 240), has great significance. 



