290 : BACTERIOLOGY. 
rise of temperature, a noticeable improvement in the 
tuberculous process results. The amount of tuberculin 
injected is continually increased, so as to continue. the 
moderate reactions. After several months all reactions 
cease, the patients having become temporarily immune 
to the toxin, but not to the:growth of the bacillus. 
Further injections are now useless until this immunity 
has passed. During the treatment the bacilli themselves 
have not been directly affected, and when the treatment 
is interrupted the tuberculous process is apt to progress. 
Many cases, however, of pure tuberculosis become cured 
or greatly benefited by several periods of treatment. 
The substances produced in the body by the old tuber- 
culin neutralized the tubercular toxins, according to 
Koch, but were not bactericidal. After a series of ex- 
periments, he considered the difficulty to be due to the 
nature of the envelope of the tubercle bacillus, which 
made it difficult to obtain the substance of the bacilli 
in soluble form without so altering it by heat or chem- 
icals that it was useless to produce immunizing sub- 
stances. He conceived that immunity was not produced 
in man for somewhat similar reasons—possibly, the 
bacilli never giving out sufficient toxin to cause cura- 
tive substances to be produced. He therefore decided 
to grind up the dried bacilli and soak them in water, 
and thus obtain, if possible, without the addition of 
heat, a soluble extract of the body-substance of the 
bacilli, which he hoped would be immunizing. He 
also tried to eliminate as much as possible of the toxic 
products which produce fever. Biichner by a different 
method, through crushing under a great pressure 
tubercle bacilli mixed with sand, and thus squeezing 
out their protoplasm, obtained a very similar substance. 
