Ill 



THE BACTERIA FOUND IN MILK 



29 



gives the following instructive table in which the percentages 

 of cowshed, retailers', and consumers' samples, giving positive 

 results in the various dilutions, are shown : 



The percentages showing a positive result are irregular, but 

 in the highest dilution increase from left to right in the table, 

 being greatest in the consumers' samples column. 



Not only are streptococci found in mixed milk, but they 

 are present in milk collected from individual cows, and drawn 

 with great care direct from the teats into sterile bottles, and 

 this even after the fore-milk has been entirely rejected. Out 

 of 88 apparently healthy cows examined by the writer, in 

 which the middle milk (of all four quarters) was examined, 

 in 46, or 52 per cent, streptococci were found when 1 c.c. 

 of the milk was examined. In some cases the streptococci 

 were scantily present but in others very numerous, agar-plates 

 brushed with O'l c.c. of milk showing thousands of strepto- 

 coccus colonies. 



The sources whereby streptococci are added to milk are 

 individually no doubt varied, but are mainly four in number. 



(a) The teat passages and milk cisterns of healthy cows. 

 The streptococci gain entrance by direct infection through the 

 teat mouth, and are transmitted by and multiply in the milk 

 left in the teat canal. The milk cistern becomes infected, 

 and the streptococci establish themselves. 



(5) Manurial contamination. Streptococci are very numer- 

 ous in cow manure, varying from 100,000 to 10 millions or 

 more per gramme. In view of the gross manurial pollution of 

 milk this must be regarded as their most abundant source. 



