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A MANUAL OF BACTERIOLOGY 



extract from pure cultivations of destroyed tubercle 

 bacilli. This so-called lymph contains mineral 

 salts, colouring substances, unknown extractive 

 matter, besides the dead bacilli. According to 

 Koch, some of these substances can be removed 

 from the 'lymph' tolerably easily. The effective 

 substance is mainly insoluble in absolute alcohol, 

 and can be precipitated by it, not, indeed, in a pure 



condition, but still com- 

 bined with the other 

 extractive matter, which 

 is also soluble in alcohol. 

 The colouring matter 

 may also be removed, 

 so that it is possible to 

 obtain from the extract 

 a colourless dry sub- 

 stance, which contains 

 the effective substance 

 in a much more con- 

 centrated form than 

 the original glycerine 

 solution. The effective 



FIG. 49. INJECTING KOCH'S ' LYMPH.' Substance appears to be 



a derivative from albu- 

 minous compounds, and is closely allied to them. 

 It is not a ptomaine ; but appears to be an enzyme ; 

 and tuberculin contains less than 1 per cent, of this 

 enzyme. 1 



The treatment consists in injecting, subcutane- 



1 See also Hunter's paper in British Medical Journal, 1891 

 (ii), p. 169. 



