igo2-3] Bacterial Contamination of Milk. 473 



ing, a similar examination was made of the tissues of the udder. In all 

 cases, even in the upper third of the udder, bacteria were found, and 

 they were identical with those found in the milk. He concludes that 

 •' milk, when secreted by the glands of the healthy udder, is sterile. It 

 may, however, immediately become contaminated by the bacteria which 

 are normally present in the smaller ducts of the udder." However, 

 " the bacteria so far found in the interior of the udder do not affect milk 

 seriously. This, however, does not preclude the possibility that forms 

 more injurious to milk may invade the udder." 



From the above resume it is apparent that widely different results 

 have been obtained by different investigators, and it has been a very 

 interesting study to see whether the experiments conducted at Guelph 

 would throw any light upon these divergencies in results. 



The plan of experiment has been as follows : For a number of days 

 samples were taken from the fore and after milk of a number of cows 

 on the College Farm. The samples were collected in sterile test-tubes, 

 and previous to taking the milk, the flank, udder, and teats of the cows 

 were thoroughly washed with a i-iooo solution of mercuric chloride. 

 Gelatine plates were then made from these samples, and afterwards the 

 number of colonies counted and the different species isolated and culti- 

 vated on the various media. It soon became apparent that while 

 several species were more or less constant in the udders of all the cows, 

 yet there were many variable species present in the milk of some cows 

 that were not present in that of others, and not even in the same udder 

 on two successive days. Therefore, in making a systematic study, it 

 was deemed best to confine our attention to those species that were 

 more or less constantly present in the milk of all the cows, and to make 

 a complete study of those existing in the udder of one particular cow. 



The number of bacteria present in both the fore and after milk of 

 the various cows, and of the same cow, and even in the different 

 quarters of the udder of the same cow, were so widely different that 

 little stress can be laid upon an exact enumeration. 



The following samples, which are typical of many others, will 

 illustrate the point : 



Cow No. I. Determination i. 



Fore-milk, rig-ht front teat 86,400 per c.c. 



" " hind " 120,000 " 



Strippings, " front " 40,800 '* 



" " hind " 57,000 " 



