ITBLIC PROBLEMS l8l 



determination of the relative numbers of the different types of 

 bacteria enables us to draw some useful conclusions as to the 

 age and purity of the milk. Such an analysis is also very useful 

 when the attempt is being made to locate the source of special 

 troubles that a cheese factory may experience. 



The method of making such a qualitative analysis is given 

 on page 304. To make it of any value it is necessary to know 

 how to interpret the results. 1 To do this intelligently requires 

 considerable experience with the work, but a few general rules 

 can be given. 



The first thing to do is to estimate in percentages each of the 

 types found. Then, in determining the meaning of the different 

 percentages, the following facts should be considered: If the 

 number of bacteria is very high, 5,000,000 to 20,000,000, the 

 percentage of Bact. lactis acidi should range from 20 per cent, 

 to 50 per cent. If the percentage is lower than this, it indicates 

 that this large number of bacteria contains many suspicious 

 organisms, and that the milk should be condemned. If the per- 

 centage is as high as 80 to 90 per cent., the milk may be re- 

 garded as unsuspicious, even though the number of bacteria 

 mount up into many millions. If the original sample has only 

 a few hundred thousands, little inference can be drawn as to 

 the healthfulness of the milk from the percentage of types of 

 bacteria. If, however, the number of liquefiers is high, it in- 

 dicates excessive filth contamination, while, if these are few 

 and the acid organisms numerous, it indicates a high quality 

 of milk. Large numbers of liquefiers are always an indication 

 of undesirable filth contamination. These specifications are not 

 very definite, but they cannot be made more definite from the 

 fact that at present a more accurate qualitative analysis appears 

 to be impractical. 



1 Conn and Esten. Ann. Rep. Storrs Exper. Sta., 1903-3. 



