168 PATHOGENIC ORGANISMS 



Pseudo-tuberculosis. Milk occasionally contains organisms 

 capable of producing chronic lesions which partially simulate 

 those of B. tuberculosis and to which the designation of pseudo- 

 tuberculosis has been given. Delepine found that amongst 

 these infections was one resembling chronic pyaemia, but in his 

 opinion the resemblance is superficial and no experienced pathol- 

 ogist could mistake such lesions in the guinea pig for true 

 tuberculous lesions; also that an experimenter with scanty 

 pathological experience could not make a mistake if the or- 

 ganisms in the lesions are microscopically examined. The 

 finding of the giant cells, characteristic of true tuberculosis, in 

 histological sections would also clear up doubtful microscopic 

 diagnoses. 



In pigs that have been kept for five to six weeks the chronic 

 lesions due to B. abortus may be found, but as this organism is 

 not acid fast there is no difficulty in eliminating this possible 

 source of error. 



Bovine and Human Types of B. Tuberculosis. The differ- 

 ence in the cultural and other characteristics of these types is 

 essentially relative rather than absolute and this fact must 

 always be kept in mind when attempting to classify cultures of 

 B. tuberculosis. 



Eastwood and Griffith 38 classified cultures as dysgonic or 

 eugonic according to the luxuriance of the growth on glycer- 

 inised agar and they found that the dysgonic type was usually 

 of high virulence for rabbits and corresponded to the bovine 

 type. The human type grew well on glycerine-agar but pos- 

 sessed much lower virulence for rabbits. The chief differences 

 in the two types may be summarised as follows : 



BOVINE. HUMAN. 



Morphology. Only slight differences can be found, the bovine organisms 

 being usually shorter, straighter, and thicker. 



Cultural characteristics. 



Glycerine-agar. Grows feebly and Grows luxuriantly and usually 

 with development of discrete col- without difficulty. Growth 



onies. often wrinkled. 



