394 



EXPERnilJXTAL FA RJfS 



5 GEORGE v.. A. 1915 



Petri disli. Tlie Agar medium was cooled to about 40°C. and poured into the dish, 

 the whok' being' then mixed and .spread over the pLate. The plates were then placed 

 in the incubator at o7°C. and left for forty houi-s. This is a long incubation period, 

 a fact which should be remembered in considering results. Two plates were used 

 with each, sample, to check results. It was found that the dilution used (200: 1) was 

 convenient, the colonies spreading out well and being easily counted. This is the 

 melhod followed by W. IF. Park, N.Y. (Journal of Hygiene, July, 1901). The 

 following table show? the results of the first series of tests :— 



Tabi.k " A." 



With regard to the first column of figures, it may be observed that the milk 

 drawn directly from the udder is not often sterile. 



Five counts were discarded, it being clear in these cases that accidental contamina- 

 tion had occurred. Thus on February 24 the milk of Xo. 29 showed 6,600 per c.c. 

 from the teat, and only 4,000 in each of the samples from pail and cooler. Again, on 

 February 28, No. 10 showed 30,000 in the milk from the teat, and 20,000 in the milk 

 from the pail. The first sample was obviously contaminated from some other source. 

 Such counts as these, where an error was qlearly indicated, were therefore discarded. 

 The average of the fifteen counts tabulated gives:— 



Milk taken directly from teat contained per c. c. l,.yS7 



." " pail contained per c. c. 5,154 



" " cooler contained.." per c. c. 10.987 



Reducing this to a percentage we have the following facts indicated: — 



Process 1. — Milking 224 per cent increase. 



Process 2. — Cooling and straining 113 per cent increase. 



The value of these figures is relative. Quantitative tests of bacteria cannot bo 

 taken too literally. Yet it will be seen from the table gi^•en above that the results are 

 quit« uniform, and are to be relied upon as far as they go. They will in any case serve 

 to emphasize, the fact that each additional handling of milk greatly increases the risk 

 of contaVii nation, even where clean methods are followed; and consequently, that sim- 

 plicity and quickness of handling are of prime importance in producing clean milk.^ 



Agassiz. 



