PROTECTIVE INOCULATIONS. 361 
taneously into guinea-pigs. The experiments of Lite also indicate 
that an “attenuation of virulence” has occurred in the cultures pre- 
served in Koch’s laboratory, originating in 1882 from the lungs of a 
tuberculous ape. The author named made experiments with cultures 
from this source (ninetieth to ninety-fifth successive cultures), and at 
the same time with a culture obtained from Roux, of Pasteur’s labor- 
atory. Rabbits inoculated with cultures from the last-mentioned 
source developed a hectic fever at the end of two weeks, and died tu- 
berculous at the end of twenty-one to thirty-nine days. Twelve rab- 
bits were inoculated with the cultures from Koch’s laboratory; the 
injections were made either subcutaneously, or into a vein, or into the 
pleural cavity, or into the cavity of the abdomen. No elevation of 
temperature occurred in any of the animals, and they were found at 
the end of a month to have increased in weight. At the end of six 
weeks one of them was killed and tubercular nodules were found in 
various organs. The remaining animals were killed at the end of 
one hundred and forty-four to one hundred and forty-eight days. 
The two inoculated subcutaneously presented no sign of general tu- 
berculosis, but a small yellow nodule containing bacilli was found at 
the point of inoculation. Those inoculated by injection into a vein 
showed one or two nodules in the lungs containing a few bacilli. In 
Koch’s original experiments rabbits were killed by intravenous inocu- 
lation of his cultures in from thirteen to thirty-one days. That this 
attenuation of virulence depends upon a diminished production of 
toxic product to which the bacillus owes its pathogenic power appears 
to be very certain, in view of the fact that the late cultures in a series 
have a more vigorous and abundant development than the more patho- 
genic cultures obtained directly from the animal body. 
The discovery by Koch of a toxin in cultures of this bacillus, 
which is soluble in glycerin, and which in very minute doses pro- 
duces febrile reaction and other decided symptoms when injected 
subcutaneously into tuberculous animals, must rank as one of the first 
importance in scientific medicine, whatever the final verdict may be 
as to its therapeutic value in tuberculous diseases in man. 
The toxic substance contained in Koch’s glycerin extract from cul- 
tures of the tubercle bacillus, now generally known under the name of 
tuberculin, is soluble in water, insoluble in alcohol, and passes readily 
through dialyzing membranes. It is not destroyed by the boiling 
temperature. According to the chemical examination of Jolles, the 
“lymph” contains fifty per cent of water and does not contain alka- 
loids or cyanogen compounds. It contains albuminates, which are 
thrown down as a voluminous white precipitate by tannic acid, and 
