Invasion of the Udder by Bacteria. 285 



dishes, where it again became solid. Agar plate cultures were made 

 from the milk samples, and, together with those slanted agar cuh 

 tures already inoculated, were placed in the incubator. - The agar 

 plate cultures were designed to be used as a check upon the reli- 

 ability of the conclusions reached from an examination of the other 

 cultures. For instance, it might be possible than organisms which 

 appeared to have been obtained from the interior of the udder may 

 have lodged upon the bits of tissue during the transfer. The iden- 

 tity in cultural and morphologic characters of bacteria found in the 

 fore milk and in the glandular tissue of the udder would largely 

 eliminate a source for false conclusions. 



The tubes of slanted agar, after standing in the incubator for 

 several days, were examined particularly with reference to the 

 presence or absence of growth. I^ote was taken of the color and 

 character of the growth of the colonies, and sub-cultures were 

 made. 



The gelatin plate cultures ^ were in like manner examined, and 

 furnished a more satisfactory method for obtaining pure cultures. 

 With these, a direct comparison made it possible to trace the pres- 

 ence of the same organism in the three localities. In order to prove 

 that these identities existed, sub-cultures were made for a more 

 detailed comparison later. The plate cultures made from the milk 

 were examined and sub-cultures were made from all of the appa- 

 rently different colonies. 



In the examinations of udders Y and 8, bits of tissue were brought 

 to the laboratory in sterile test tubes. They were then placed in 

 cool liquid agar and treated thereafter similar to gelatin. The 

 results from this use of agar were less satisfactory than those from 

 gelatin, since the growth of most species is less distinctive upon 

 agar. 



* The gelatin plate pictured on the first cover page gives an idea of the num- 

 ber of colonies occurring in the cultures made from the glandular tissue of the 

 udder. The culture was rather old when photographed. Hence the colonies 

 are larger and have become more confluent than when first examined. The bit 

 of glandular tissue may be seen as an irregular shaped black area near the center 

 of the plate culture, The illustration is about one-half the diameter of the 

 original plate. 



