THE CAUSE OF TUBERCULAR DISEASE. 259 



animals, and, without exception, it was found that the injection of the 

 parasite into the animal system was followed by decided and, in most 

 cases, virulent tubercular disease. 



In the cases thus far mentioned inoculation had been effected in 

 the abdomen. The place of inoculation was afterward changed to the 

 aqueous humor of the eye. Three rabbits received each a speck of 

 bacillus culture, derived originally from a human lung affected with 

 pneumonia. Eighty-nine days had been devoted to the culture of the 

 organism. The infected rabbits rapidly lost flesh, and after twenty- 

 five days were killed and examined. The lungs of every one of them 

 were found charged with tubercles. Of three other rabbits, one re- 

 ceived an injection of pure blood-serum in the aqueous humor of the 

 eye, while the other two were infected in a similar way, with the same 

 serum, containing bacilli, derived originally from a diseased lung, and 

 subjected to ninety-one days' cultivation. After twenty-eight days 

 the rabbits were killed. The one which had received an injection of 

 pure serum was found perfectly healthy, while the lungs of the two 

 others were found overspread with tubercles. 



Other experiments are recorded in this admirable essay, from which 

 the weightiest practical conclusions may be drawn. Koch determines 

 the limits of temperature between which the tubercle-bacillus can 

 develop and multiply. The minimum temperature he finds to be 86 

 Fahrenheit, and the maximum 104. He concludes that, unlike the 

 bacillus anthracis of splenic fever, which can flourish freely outside 

 the animal body, in the temperate zone animal warmth is necessary for 

 the propagation of the newly discovered organism. In a vast number 

 of cases, Koch has examined the matter expectorated from the lungs 

 of persons affected with phthisis and found in it swarms of bacilli, 

 while in matter expectorated from the lungs of persons not thus 

 afflicted he has never found the organism. The expectorated matter 

 in the former cases was highly infective, nor did drying destroy its 

 virulence. Guinea-pigs infected with expectorated matter which had 

 been kept dry for two, four, and eight weeks respectively were smitten 

 with tubercular disease quite as virulent as that produced by fresh ex- 

 pectoration. Koch points to the grave danger of inhaling air in which 

 particles of the dried sputa of consumptive patients mingles with dust 

 of other kinds. 



It would be mere impertinence on my part to draw the obvious 

 moral from these experiments. In no other conceivable way than that 

 pursued by Koch could the true character of the most destructive 

 malady by which humanity is now assailed be determined. And, how- 

 ever noisy the fanaticism of the moment may be, the common sense of 

 Englishmen will not, in the long run, permit it to enact cruelty in the 

 name of tenderness, or to debar us from the light and leading of such 

 investigations as that which is here so imperfectly described. 



