304 BACTERIA PATHOGENIC TO MAN 



and inorganic salts. The true nature of the toxic substances is not known. 

 It keeps well, retaining its activity indefinitely. 



The method of treatment and the results obtained from the old 

 tuberculin have been described by Koch briefly as follows: After each 

 injection, which should be large enough to cause a slight but not a 

 great 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. Some cases, however, of pure tuberculosis of moderate 

 extent become cured or greatly benefited by several periods of treatment. 

 When the seat of tuberculous lesions is visible, as in lupus, a moderate 

 dose of tuberculin causes a visible inflammatory reaction, which may 

 result in necrosis and a casting off of the infected tissue. The bacilli 

 themselves are not killed. 



According to Koch, the substances produced in the body by the old 

 tuberculin neutralized the tuberculous toxins, but were not bactericidal. 

 After a series of experiments 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 chemicals that it was useless to produce immunizing 

 substances. He conceived that immunity was not produced in man 

 for somewhat similar reasons possibly the bacilli never giving out 

 sufficient toxin to cause curative substances to be produced. He there- 

 fore 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 immun- 

 izing. He also tried to eliminate as much as possible of the toxic prod- 

 ucts which produce fever. Buchner 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. 



The new tuberculin formed by either of these methods is a watery 

 extract of the soluble portions of the unaltered tubercle bacilli. As 

 can be readily seen, in a preparation thus made, contamination is difficult 

 to avoid, freedom from intact bacilli is uncertain, and the strength of 

 the solution prepared at different times is variable. Twenty per cent, 

 of glycerin is added to preserve the tuberculin from contamination. 

 After three years of trial the results obtained with the new tuberculin 

 preparations cannot be considered to have exerted either very different 

 or very superior effects to the older product. 



As to the results obtained in general the reports are as yet conflicting. 

 Lupus seems to be decidedly benefited for a time both by the old and 

 the new tuberculin. Relapses are, however, common. On advanced 



