364 PROTECTIVE INOCULATIONS. 
best results were obtained when the potatoes were wet with a five-per- 
cent solution of glycerin. The sections of potato were placed in Petri’s 
dishes upon blotting paper wet with a sublimate solution, and the 
dishes containing the cultures were surrounded with cotton wet with 
the same solution. The cultures were subsequently treated with dis- 
tilled water, to extract the active principle, which was also obtained 
from the bacilli by mixing them with glycerin in the proportion of 
1:10. 
Numerous experiments have been made with dead tubercle bacilli, 
as well as with the toxic products developed in cultures. Héricourt 
and Richet (1890) found by experiment that old cultures heated to 80° 
C., several days in succession, when injected into a vein in rabbits, in 
the dose of ten to twenty cubic centimetres, caused the death of these 
animals. Smaller doses from which the animals recovered seemed to 
make them less susceptible to infection than control animals, but the 
number of experiments was too limited to establish this as a fact. In 
a subsequent (1891) communication the authors named claim to have 
succeeded in immunizing rabbits by injecting filtered and sterilized 
cultures of the tubercle bacillus, either subcutaneously (five to fifteen 
cubic centimetres) or into a vein (twenty to forty drops). The injections 
were repeated every second or third day for a period of fifteen days, 
after which the test inoculation was made with a culture, obtained 
from a tuberculous cow in one series, and from tuberculous fowls in 
another. Four vaccinated rabbits in the first series escaped general 
tuberculosis, while four out of eight control animals died tuberculous. 
In the second series five vaccinated animals resisted infection and 
three out of four control animals died tuberculous. 
De Schweinitz (1894) has reported the results of experiments with 
attenuated cultures of the tubercle bacillus, and has, apparently, suc- 
ceeded in conferring immunity upon guinea-pigs by inoculations 
with such cultures. 
Klebs (1891), in experiments on guinea-pigs and rabbits, convinced 
himself that the fatal result of an inoculation with tubercle bacilli (in 
the cavity of the abdomen or subcutaneously in guinea-pigs, and in 
the eye in rabbits) was greatly delayed by injections of Koch’s tuber- 
culin (0.3 to 0.5 cubie centimetre) either before or after infection. 
Baumgarten (1891), in experiments upon rabbits inoculated with 
tubercle bacilli in the anterior chamber of the eye, failed to obtain 
favorable results from treatment with Koch’s tuberculin given in con- 
siderable doses (0.5 to one gramme) either before or after infection. 
The results reported in the same year by Gramatschikoff, by 
Popoff, by Alexander, and by Gasparini and Mercanti, were also un- 
