264 TUBERCULOSIS 



true not only of man but of many species of animals used in 

 experimental inquiries, that many individuals are on the border- 

 line between immunity and susceptibility. From the wide 

 spread of the bacilli in centres of human population, it is certain 

 that the opportunity for infection arises in a very large propor- 

 tion of the race ; in many cases no results follow infection, and 

 in many others small lesions occur which do not develop further ; 

 this has actually been shown by morbid anatomists to be the 

 case. The disease being thus so often characterised by transient 

 local effects without constitutional disturbance, the course of an 

 immunisation may be expected to be 'rather different from that 

 obtaining in an ordinary acute affection, though the underlying 

 processes may be of the same nature. It is difficult, for instance, 

 on account of the slowness of tubercular processes, to define 

 recovery from an attack of the disease, or to speak of an animal 

 recovering from the effect of an inoculation during an immunisa- 

 tion. It follows that little is known regarding an attenuation 

 of the tubercle bacillus analogous to what is an important 

 feature in immunisations against other organisms. It has 

 been thought by some that the tubercle bacilli from so-called 

 scrofulous glands are less virulent than those, say, from phthisis, 

 but apparently here sufficient attention has not been paid to the 

 difference of the numbers of bacilli injected in each case, and 

 this appears to be a very important point. Experiments have 

 also been brought forward which appear to show that the injec- 

 tion of bacilli from avian tuberculosis could protect the dog 

 against bacilli derived from man. But these are not yet conclusive. 



Agglutinative Phenomena. 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, commencing 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 leave the 

 mixture for 24 hours before observing. As with other agglutina- 

 tive observations, it is difficult to correlate the degree of agglu- 

 tinating power of the serum with the degree of immunisation 

 possessed by the individual from which it was derived. 



Antitubercular Sera. Several attempts have been made to 

 treat tuberculosis with the serum of animals immunised by the 

 tubercle bacillus or its products. The most successful is perhaps 

 that of Maragliano. This author distinguishes between the 

 toxic materials contained in the bodies of the bacilli (which 

 withstand, unchanged, a temperature of 100 C.) and those 

 secreted into the culture fluid (which are destroyed by heat). 



