150 APPLIED BACTERIOLOGY 



alcohol, and he found that it was apparently due to these 

 substances which rendered the reabsorption of the bacilli 

 so difficult in the animal body. As a result of his investi- 

 gations, Koch announced that he has prepared three new 

 modifications of the original tuberculin. These he names 

 respectively Tuberculin A, 0, and R, and for their pre- 

 paration it is necessary to employ virulent cultures. 

 Tuberculin A is prepared by extracting the bacilli with deci- 

 normal soda solution, neutralising, and filtering. This acts 

 very much like ordinary tuberculin, but the reaction is 

 much more severe. Tuberculin is prepared by drying 

 and pounding tubercle bacilli, and extracting with distilled 

 water ; the emulsion is then centrifugalised. The residue 

 left in the centrifuge from the last operation is dried, 

 pounded in an agate mortar, and extracted with water as 

 before, these processes being repeated until hardly any 

 solid residue is left. The whitish opalescent liquids re- 

 sulting from these operations are mixed, and the result is 

 Tuberculin R. 



Tested on animals, the Tuberculin produced almost 

 identical effects with the alkaline extract (Tuberculin A)j 

 except that no abscesses are produced at the seat of inocu- 

 lation. It had, however, but little immunising effect. The 

 Tuberculin R, on the contrary, possesses very decided im- 

 munisation effects, with but little reaction. This compara- 

 tive absence of reaction is a great improvement upon the 

 original tuberculin. The preparation by hand of the last 

 preparation is not unattended by risk, but it can be per- 

 fectly well made by machinery, and is manufactured under 

 Dr. Koch's direction by the firm of Meister Lucius and 

 Briining, of Hochst-on-the-Main. The use and doseage of 

 the preparation (Tuberculin R) is simple. The fluid is 

 made to contain 10 milligrammes of solid matter in the 

 cubic centimetre. This is diluted with sterile salt solution 



