66 MASTITIS OF THE COW 



The colon cultures have a strong, unpleasant, burnt 

 odor. 



Resistancy. — The colon bacillus does not form spores 

 but is nevertheless very resistant. It can live a year in a 

 culture kept in the dark and sealed to prevent drying. 



Pathogenicity. — The virulence is very variable. In 

 subcutaneous inoculations of laboratory animals certain 

 colon bacilli manifest no alterations. Others produce only 

 a local necrosis with abscess formation, while others may 

 kill the animal more or less quickly. 



As a rule, laboratory animals die of bactersemia. 



On autopsy one finds a more or less enlarged spleen, 

 and the point of inoculation in the subcutis is oedematously 

 swollen or manifests necrosis with inflammation in the sm'- 

 rounding tissue. There are no other distinct lesions. 



Mice are very susceptible to the infection. They may 

 die in from one to twelve days. As a rule they die in about 

 three days, seldom after a coui'se of a week or more. 



A dog inoculated subcutaneously with a virulent culture 

 did not die but showed a necrotic nodule at the point of 

 inoculation. 



A guinea-pig was inoculated subcutaneously with a 

 virulent cultm-e and showed a widespread severe oedema- 

 tous swelling at the point of injection and also bacteraemia. 



A pigeon inoculated in the pectoral muscle with a viru- 

 lent culture did not die but developed a necrotic nodule at 

 the point of injection. 



Cows. — About six months after calving a cow was in- 

 jected in one teat with 10 c.c. of a one-day-old bouillon 

 culture of colon bacillus which had previously been isolated 

 from a case of mastitis. Of the two control mice one died 

 in two and the other in three days. 



Examination of the quarter before infection showed no 

 alterations. The milk was of normal appearance but con- 

 tained a small quantity of sediment consisting of yellow 

 pus which contained a few streptococci. 



