and Laboratory Methods. 2031 



was ascertained that at the time of parturition the placentae had been retained 

 by a number of cows, and these had been allowed to decompose in the uterus. 

 It was soon after this that the " gassy " curd began to appear. A thorough 

 bacteriological examination located the bacillus which was the cause of the 

 " gassy " curd in the udders of the cows of the herd ; and it seemed very prob- 

 able, though of course not demonstrable, that it had gained access to the udders 

 from the decaying placentae. 



Subsequent to this, Ward conducted further experiments, and in an article 

 on "The Persistence of Bacteria in the Milk Ducts of the Cow's Udder,"^^ he 

 concludes (1) " certain species of bacteria are normally persistent in particular 

 quarters of the udder for considerable periods of time, and (2) it is possible for 

 bacteria to remain in the normal udder and not be ejected along with the milk." 

 These conclusions contravert the statement previously made by Von Freuden- 

 reich and Grotenfeldt that the milk ducts are always sterile at the close of milk- 

 ing, becoming tenanted from the outside alone by organisms which chance to 

 come in contact with the end of the duct. 



The results of still later investigations by the same author are published in a 

 bulletin! ^ on "The Invasion of the Udder by Bacteria." In these investiga- 

 tions, a bacteriological examination was made of the udders of milch cows 

 slaughtered after reacting to the tuberculin test. In all cases the udders were 

 perfectly normal. Just before slaughtering the animals were milked as thoroughly 

 as possible, and samples of the milk taken and a bacteriological examination 

 made. After slaughtering, 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 gland 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 apparently 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 various 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 

 1-1000 solution of mercuric chloride. Gelatin plates were then made from these 

 samples, and afterwards the number of colonies counted and the different 

 species isolated and cultivated 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 



