328 BACTERIA PATHOGENIC TO MAN 



as the latter and become more quickly indistinguishable. Isolated 

 colonies, especially those in the neighborhood of xerosis bacilli or 

 staphylococci, grow larger and their contour is slightly wavy; they are 

 more opaque and granular than influenza colonies. In serum or 

 blood bouillon a slight cloudiness is produced which finally settles 

 down. 



Resistance. In culture media the bacilli die rapidly, seldom living 

 more than five days. Development ceases at 20. They resist a 

 temperature of 50 for ten minutes, but cannot withstand 60 for more 

 than one or two minutes. Kept for one and a half hours at 7 they 

 still remain alive. Exposure to the sun's rays for one-half hour does 

 not kill them, but at the end of two and one-half hours they die. They 

 cannot resist dying for any length of time. 



Transmission. This occurs only by contact either by direct or indirect 

 conveyance of the moist infective material. Infection is not communi- 

 cated through the air by means of dust, as the bacilli soon die when 

 dried. It may, however, be conveyed by flies, etc. 



Pathogenesis. The Koch- Weeks bacillus is not pathogenic for ani- 

 mals. Man, on the contrary, is extremely susceptible to infection from 

 this bacillus, which produces one of the most contagious diseases 

 known. 



Immunity is not produced to any extent by one attack, but there 

 does seem to be an individual susceptibility to the disease. 



Differential Diagnosis. The only micro-organisms from which the 

 Koch-Weeks bacillus would seem to require differentiation are the 

 influenza bacillus of Pfeiffer, the so-called influenza bacillus of con- 

 junctivitis of Miiller and the pseudoinfluenza bacillus of Zur Nedden. 

 These latter bacilli, however, grow well only on hsemoglobin media, 

 which the Koch- Weeks bacillus does not require. The colonies on 

 serum agar are smaller than those of the influenza bacilli and the 

 edges are more granular. While the influenza bacillus is slightly 

 pathogenic for certain animals, the Koch-Weeks bacillus has so far 

 given negative results with all animals. Clinically also the disease is 

 distinctly different. 



