308 MILK 



chine-drawn milk had a higher germ content than hand-drawn 

 milk when the following methods of cleaning were employed: 

 Cleaning the machine by pumping water through it; placing the 

 cups after cleaning the machine in a solution of Gold Dust 1 : 300; 

 and by using borax in the cleaning fluid. When the parts of the 

 machine were sterilized in steam the germ content of machine- 

 drawn milk was still somewhat higher than in hand-drawn milk. 

 And even when the rubber parts were placed in a 10 per cent, 

 sodium chlorid solution after the machine had been washed the 

 bacteria were more numerous in machine-drawn milk than in 

 hand-drawn milk. Good results were obtained when 2J per cent, 

 of formalin were used for cleaning, and still better results with 

 3.5 per cent, formalin. In the latter case the parts were prac- 

 tically sterile. 



Strong brine has been recommended by manufacturers of 

 milking machines as a suitable antiseptic for keeping the rubber 

 parts of the machine between milking periods. Stocking and 

 Mason, however, found that when the salt solution was three 

 days old it contained 1000 to 2000 bacteria per cubic centimeter. 



An important factor came to light in the experiments of Stock- 

 ing and Mason. It has been stated before that milking machines 

 operate by alternating suction and admission of air for relief of 

 the vacuum. This air, of course, comes from the stable and from 

 the immediate environment of the cow. It therefore contains 

 many bacteria. By filtering the relief air through absorbent cot- 

 ton impurities were eliminated and satisfactory results obtained. 

 This is illustrated in the following table given by the authors: 



INFLUENCE OF COTTON RELIEF FILTERS ON THE GERM CONTENT OF MACHINE-DRAWN 



MILK 



With cotton filters 



Without cotton filters . . . 



Total bacteria. Acid forming. Liquefiers. 



Rapid. Slow. 



Machine 1,578 662 14 80 



Hand 4,560 1142 18 280 



Machine 11,541 5209 22 238 



Hand 7,467 3226 40 181 



The effect of cotton filters is clearly shown not only in regard 

 to total numbers of bacteria but also in regard to groups. Acid- 

 forming bacteria and liquefiers were less numerous, as were total 

 numbers. 



Results obtained by Haecker and Little showed also that low 

 bacterial counts can be obtained by machine milking, but only 

 when all parts are thoroughly cleaned. 



Meek again found that machine-drawn milk contained about 

 twice as many bacteria as hand-drawn, but Hastings and Hoff- 

 mann after a series of tests concluded that machine-drawn milk 

 and hand-drawn milk contained about the same number, possibly 



