362 THE BACILLUS OF TUBERCULOSIS 



mode of surface growth of tubercle bacilli was shared by all mam- 

 malian races examined by Smith after they had acquired a certain 

 saprophytic habit, and the process is well known to all who have 

 cultivated tubercle bacilli for the preparation of tuberculin. If 

 ordinary bouillon prepared from fresh beef to which 3 to 5 per cent, 

 glycerin has been added is used, and if the acidity is made equiva- 

 lent to about 2 per cent, of normal acid, phenolphthalein being the 

 indicator, the reaction of the bouillon during the formation of the 

 membrane will take one of two directions. It may approach the 

 neutral point and reach an acidity or an alkalinity of about 0.1 to 

 0.2 per cent, when the membrane is complete and remain at this 

 point, or else the acidity may diminish during the first months, 

 increase again during the second, and fluctuate more or less if the 

 observation is continued, but the reaction does not reach the neutral 

 point. In the human cultures, on the other hand, the reaction curve 

 also moves toward the neutral point, but soon swings back to a greater 

 acidity. 



The human type of tubercle bacillus has very slight virulency 

 toward cattle. This fact may indeed be considered as established. 

 It has been proved beyond question that human sputum bacilli used 

 on cattle in doses in which bovine bacilli will produce general tuber- 

 culosis have, as an almost universal rule, practically no lasting effects 

 whatever. Bovine tubercle bacilli are likewise more virulent than 

 the human type toward guinea-pigs, rabbits, mice, rats, sheep, goats, 

 pigs, dogs, equines, etc. Rabbits are particularly well adapted to 

 show the difference in virulency between the bovine and human 

 types when applied to the same species of animals. According to 

 Weber, 0.001 gr. of bovine bacilli injected intravenously kills rabbits 

 with the production of a general tuberculosis in three weeks, while 

 the human type under the same conditions produces a very chronic 

 slow form of tuberculosis only after months. The first extensive 

 experiments showing that such is the action of human sputum 

 bacilli toward cattle were made by Koch and Schiitz. Upon the 

 basis of these observations Koch, in 1901, before the British Congress 

 on Tuberculosis appears to have taken the standpoint that the 

 danger of transmitting bovine tuberculosis to man is practically nil. 

 After 1901, however, it was ascertained, and Ravenel had, indeed, 

 made some observations before this time, that tubercle bacilli 

 of the bovine type, very virulent 1 to cattle, are found in certain 

 tubercular lesions in man. Such bacilli, however, with a possible 

 single exception (Arloing), have never been found in the sputum of 

 tubercular patients, and since human sputum bacilli were exclusively 

 used in the early experiments of Koch and Schiitz the former was 

 induced to draw conclusions which were too radical and which 

 cannot be upheld at the present time. Koch, in 1908, at the Inter- 



1 Ravenel found such bacilli in the mesenteric glands of a child. 



