400 Bulletin 165. 



ticularly that dislodged from the udder, unclean utensils and 

 faeces. For study of the species present in the air of the stable, 

 Petri dishes* containing a layer of nutrient agar were used. The 

 agar surface of each was exposed to the air for a definite length 

 of time. The bacteria in the air, thus coming in contact with 

 the agar, would later manifest their presence by the colonies 

 formed as a result of their rapid multiplication upon this medium. 

 One Petri dish was exposed under the udder of each cow at some 

 time during the period of milking, the cover of each being off 

 for a period varying from one-fourth to one-half minute. After 

 four or five days at a low temperature a slight growth was 

 observed. Had Bacillus ladis viscosiis been present, its growth 

 would have been visible much sooner. The several species which 

 did grow on the agar at that low temperature were quite unlike 

 the one sought. Sterile milk was inoculated with bits of rub- 

 bish from the floor of the stable, dust from the beams overhead, 

 cow hair, water from the drinking trough, and saw^dust from the 

 ice house. None of the samples of sterile milk thus artificially 

 contaminated became ropy, although all underwent some sort of 

 fermentation. Cultures were made from the faeces of a cow, but 

 the bacteria found threw no light upon the problem. 



An examination of all of the other probable sources from which 

 the bacteria might have gained entrance to the milk having 

 revealed nothing, attention was turned to the utensils with 

 which the milk came in contact. It would be a very simple mat- 

 ter for a milk vessel which had once contained ropy milk and 

 which had not afterward been properly cleansed, to again infect 

 normal milk placed in it. 



Upon one occasion the milk aerator in use at the farm barn 

 was found in an unclean condition, it having been carelessly 

 rinsed when last used. Cultures were made directly from the 

 milk remaining in the apparatus. Several small quantities of 

 sterile milk were exposed to infection in the pails used for milk- 

 ing and also by pouring through the mesh of the strainer pail. 

 Inoculations were made directh^ to culture media from the accu- 

 mulated mass of filth on the border of the brass strainer. Such 



*A Petri dish is a flat, shallow, circular glass vessel with sides perpendic- 

 ular to the base and provided with a closely fitting cover of the same shape. 



