234 PATHOGENIC BACTERIA IN MILK 



here as it bears directly upon the virulence of tubercle bacilli 

 passing through the alimentary canal. It is to the effect that 

 experiment shows that the tubercle bacillus can withstand the 

 action of the gastric juice. Falk and Wesener both, worked at this 

 subject, placing human tubercular sputum with artificially prepared 

 gastric juice, with the result that the bacillus was not affected. 

 Wesener took the additional precaution of keeping the emulsion at 

 blood-heat for a number of hours. Cadeac and Bournay, and 

 Strauss and Wurtz, have also investigated this subject, the two 

 latter in a most thorough manner. They employed natural gastric 

 juice, and tested its effect on pure cultures of the bacillus on glycer- 

 ine-agar. After six hours the bacilli were found on inoculation to 

 be uninjured. From these facts it may be concluded that tubercle 

 bacilli voided in the excreta of cows having intestinal tuberculosis 

 have not lost their virulence owing to any supposed germicidal 

 effect of the gastric juice. 



Tubercle bacilli of bovine and human origrin compared. — 

 The morphology of the bacilli in cultures of bovine origin is more 

 uniform and constant than in cultures from man. The bovine 

 bacilli are thicker, straight, and short, seldom more than 2 fx. in 

 length, and averaging less (Theobald Smith). In the early 

 generations many individuals are seen which are oval, their length 

 not more than double their breadth. They are less granular than 

 those from a human source. They stain evenly and deeply 

 with carbol-fuchsin, beading being almost always absent from 

 young cultures, and often from old ones. 



The human bacilli are, on the other hand, much longer, thinner, j 

 and tend to increase in length in sub-cultures. They are generally] 

 more or less curved, sometimes showing S-shaped forms. Theyj 

 stain less intensely with carbol-fuchsin, but beading is generally' 

 seen, even in early growths, and is often very well marked. 



The above characteristics are most evident and persistent in; 

 cultures grown on blood-serum. On glycerine-agar, glycerine- 

 bouillon, and glycerine-potato, bovine and human tubercle bacilli] 

 approach each other in cultural features and morphology muchj 

 more closely, and by continued cultivation the differences tend] 

 to become obliterated. Bovine cultures are more difficult tc 

 isolate than human, are apt to grow as discrete colonies in th« 

 first culture, and for several generations grow in a thin layei 

 which somewhat resembles ground glass. The optimum tempera- 

 ture and the thermal death-point are practically the same in botl 

 forms. 



