204 BACILLUS TUBERCULOSIS. 



lent tubercle bacilli, and that the disease may thus be produced 

 in persons who, up to that time, have been free from it. The 

 first-named objection is given considerable credence by those 

 whose experience in the use of tuberculin has been very 

 limited. Clinicians who have used tuberculin as a diagnostic 

 agent very freely are outspoken in their opinion that it never 

 produces disease where there is none, nor does it arouse a 

 latent tuberculosis into fatal activity. As to the second 

 objection, that can easily be overruled, because the manufact- 

 urers of tuberculin are extremely careful in its preparation, 

 testing it on guinea-pigs before it is marketed. Anders has 

 used the tuberculin-test in a large number of cases, and his 

 experience has been exceedingly satisfactory. The same is 

 true of Wood, who had charge of the Cook County (Illinois) 

 Consumptive Hospital for many years; and of many others. 



The agglutination-test has also been used as a diagnostic 

 agent, but the results have been such that little can be said as 

 to its value in diagnosis. The agglutination of the bacilli 

 occurs neither constantly nor regularly, and cannot be relied 

 upon. 



" TR " and " TO " : After a further study of tuberculin, 

 Koch came to the conclusion that its non-bactericidal action 

 was due to the very tough cell-membrane of the bacillus, 

 which prevented the body fluids from exerting any influence 

 upon it. Neither could the toxin elaborated by the bacillus 

 be carried into the tissues in sufficient quantity to cause the 

 formation of an antitoxin. Koch then conceived the idea of 

 breaking up the bacillus, either mechanically or chemically. 

 He ground up the dried bacilli very finely in a glass mortar, 

 and then made a watery extract of the soluble parts of the 

 germ. The operation of fragmenting dried bacilli in this way 

 is attended by great risks to the operator because of the pos- 

 sibility of their inhalation. This watery extract was centri- 

 fuged. The sediment he named " TR " (tuberculin residue), 

 and the supernatant clear fluid "TO" (tuberculin ober or 

 upper). This latter was found to contain the tuberculin, but 

 no bacilli, either intact or fragmented. 



The residue contained both whole and fragmented bacilli. 

 With this preparation Koch was able to produce immunity in 



