300 TUBERCULOSIS 



the serum of patients subjected to repeated tuberculin injections. 

 Another immunity phenomenon which may be observed is the 

 formation of a precipitate when some of the serum of a tuber- 

 culous patient is added to a solution of tuberculin, the mixture 

 being allowed to stand for twenty-four hours (precipitin reaction). 

 There is thus evidence in some tubercular infections of a vital 

 reaction resulting in the formation of antagonistic bodies, which 

 may include both immune-bodies and precipitin s. It may be 

 said that the sera of certain animals, e.g., rabbit and ox, when 

 mixed with tuberculin, become capable of deviating complement 

 from a hsemolytic combination. 



(2) Agglutinins. The serum of tubercular patients has been 

 found to exert an agglutinating action on the tubercle bacillus. 

 A convenient method is to add different amounts of serum, com- 

 mencing with,/ say, 1 c.c., to quantities of a dilution of the new 

 tuberculin (Bazillenemulsion) equivalent to 1 part of the 

 bacterial bodies to 10,000 of diluent, and to leave the mixture 

 for twenty-four hours before observing. As with other agglutin- 

 ative observations, it is difficult to correlate the degree of 

 agglutinating power of the serum with the degree of immunity 

 possessed by the individual from which it was derived. The 

 method has been used by some as a means of diagnosis, but its 

 value is doubtful and it is certainly inferior to the methods 

 depending on supersensitiveness. 



(3) Opsonins. The serum of most normal men and of several 

 species of animals contains opsonins to the tubercle bacillus. In 

 tubercular subjects these are frequently diminished, and to 

 obtain a standard of comparison between infected and healthy 

 subjects samples of serum from a number of persons presenting 

 no signs of tuberculosis are taken and mixed. While the 

 technique of the opsonic method presents great difficulties, it 

 may be taken that with the use of such a standard an opsonic 

 index below '8 indicates a deficiency in opsonins and an index 

 above 1*2 indicates an excess. In strictly localised tuberculosis, 

 indices from '1 to '8 are frequently found, while in tuberculosis 

 with general disturbance the index fluctuates greatly from day 

 to day, being sometimes below, sometimes above unity. 



While there is thus evidence that, when the tubercle bacillus 

 gains entrance into the body, reactions similar in nature to 

 those observed in other infections are developed, the processes 

 underlying recovery from tuberculosis are exceedingly obscure, 

 and certain factors have to be taken into consideration which 

 perhaps play a greater part in this disease than in other infec- 

 tions. One of these is the great chronicity so often observed. 



