386 SUMMARY OF CURRENT RESEARCHES RELATING TO 



render it insoluble ; it is then placed for twenty-four hours in a 

 mixture of 1 cubic centimetre of a concentrated solution of methylene- 

 blue in alcohol, 0'2 cubic centimetres of a 10 per cent, solution of 

 potash, and 200 cubic centimetres of distilled water. The preparation 

 is by this coloured blue, and on it is then placed a few drops of a 

 solution of vesuvin. This has the effect of discharging the methylene- 

 blue from all the tissue elements, but not from the bacilli. The 

 former are of a brown colour, and the blue bacilli are conspicuously 

 defined. The preparation is then treated with absolute alcohol, oil of 

 cloves, and Canada balsam, in the ordinary manner. This peculiarity 

 of being rendered visible by the combined action of methylene blue 

 and vesuvin is possessed only by the tubercle bacilli and by those of 

 leprosy. All other bacteria and micrococci, known to Koch, lose, 

 under the action of vesuvin, the blue colour which they acquire from 

 methylene-blue. This constitutes a striking instance of the pregnant 

 value of the colouring methods in thus, by quasi-chemical action, 

 bringing out differences between minute organisms which are appa- 

 rently so similar, and justifies the expectation that, by analogous 

 means, differences may be demonstrated between the organisms of 

 acute diseases which are now separable with so much difficulty and 

 uncertainty, and may be the inauguration of a new era, not only in 

 the etiological knowledge of acute diseases, but also in the organization 

 of measures for their prevention. 



The bacilli of tubercle, when rendered visible by this method of 

 double coloration, are seen as very small rods, in length about one- 

 third the diameter of a red blood-corpuscle, and in breadth about one- 

 sixth of their length. In some of them distinct spores may be seen, 

 as minute, unstained, refracting, vacuole-like structures, distinguish- 

 able, however, from the vacuoles in that at their position there is a 

 slight fusiform enlargement of the bacillus. They are most abundant 

 in recent tubercular neoplasms, and least numerous in the caseating 

 centre of old miliary tubercles. They are also visible within the 

 giant cells, usually isolated, but sometimes forming well-marked sheaf- 

 like bundles. Koch found the same organisms in the walls of tuber- 

 culous cavities, in the sputum of phthisical patients, in degenerated 

 scrofulous glands, in fungous joints, and in the bones of tuberculous 

 cattle. They were never absent from the tubercular new formations 

 produced by inoculation, even in animals of the most different 

 species. 



In order to ascertain the all-important question whether these 

 organisms are actually the materies morbi of tuberculosis, Koch has 

 carried on an extensive series of culture-experiments, which have 

 yielded the most striking results. As a culture-liquid he employed 

 sterilized blood-serum from the ox. The sterilization was effected in 

 the method recommended by Tyndall, by placing the serum in a test- 

 tube closed with a plug of wadding, and exposing it for an hour on 

 each of several successive days to a temperature of 58^ C. After this 

 had been repeated for about six days, the temperature was raised to 

 65° C, and the previously fluid serum became transformed into a yel- 



