BACTERIAL MILK ANALYSIS 251 



Streptococci in small numbers are present in most 

 market milk as shown by Heinemann, and many of the 

 short chain varieties are undoubtedly at the time 

 harmless, though by passing through animals their 

 pathogenicity may become marked. 



Long chain streptococci are considered more apt to 

 indicate inflammatory reactions, and milk containing 

 these in large numbers is certainly not a safe article of 

 diet. 



A milk should not be condemned because a few chains 

 are found together with large numbers of other micro- 

 scopic organisms in a bouillon culture but it is safer to 

 exclude a milk from the market when these three tests 

 agree : 



1. Microscopical examination of the sediment shows 

 streptococci, diplococci or cocci. 



2. The plate from the same samples shows colonies 

 resembling streptococci colonies exceeding a count of 

 100,000 to a cubic centimeter. 



3. The bouillon culture from these colonies shows 

 long-chain streptococci alone or in great excess as com- 

 pared with the other bacteria present. 



Milk showing in the stained sediment both abundance 

 of long-chain streptococci and a high leucocyte content 

 should be condemned as unsafe. 



Microscopic estimate of bacteria. A milk sediment 

 properly prepared and examined under the microscope 

 with a one-twelfth oil immersion lens gives a very fair 

 idea as to the number of bacteria present. 



It is also fairly easy to determine through the micro- 

 scopic examination what dilution will be necessary for 

 plating in order to ascertain as correctly as possible the 

 number of bacteria present. 



Detection of gas-producing organisms in milk: Wis- 

 consin curd test. The Wisconsin curd test is conducted 

 as follows : 



1. Sterilize milk containers so as to destroy all bac- 

 teria in vessels. This step is very important and can 

 be done by heating cans in boiling water or steam for 

 not less than one-half hour. 



2. Place about one pint of milk in a covered jar and 

 heat to about 98 F. 



