37^ TUBERCULOSIS 



living body are the giant and endothelial cells. In these, as 

 Metchnikoff pointed out many years ago, tubercle bacilli can be 

 seen in all stages, of degeneration, from bacilli possessed of normal 

 staining properties to mere " ghosts." Either the endothelial 

 and giant cells actually engulf the bacilli, or, what is perhaps more 

 likely, they grow round them, being stimulated to growth and 

 proliferation by the action of the same toxin which, when more 

 concentrated, leads to caseation and death. Whether any 

 opsonin is necessary for this process to occur, or whether this 

 opsonin is produced locally or makes its way from the blood, we 

 do not know. What we do know, however, is that a high opsonic 

 index does not necessarily imply that the local lesions are under- 

 going cure ; chronic tubercle, and especially lupus of some stand- 

 ing, is often associated with a very high index. But Bulloch 

 found that the cases of lupus which did well on X-ray treatment 

 (which, amongst other effects, causes a permeation of the lesions 

 with plasma) were those that had a high index, and that in the 

 cases in which it was low originally better results could be 

 obtained if it were raised by means of tuberculin injections. It 

 is, therefore, not improbable that opsonin may actually soak 

 through the lymphoid zone and sensitize the bacilli, thus aiding 

 phagocytosis by the giant cells. But this is by no means certain. 

 The results of an injection of tuberculin are probably very 

 complex, and it is at least possible that the curative effect is 

 mainly or entirely due to the production of a local reaction in the 

 neighbourhood of the lesion, as a result of which it is flushed 

 with blood, and perhaps simply increased as regards nutrition. 

 Very small doses of tuberculin are sufficient to cause a slight but 

 definite reaction. This may be quite inappreciable in most 

 regions, but perfectly obvious in the case of tubercles of the iris, 

 which may be seen to become surrounded by a hyperaemic zone 

 after injections of T ^-^ milligramme of new .tuberculin, or even 

 less. Reactions of this nature are, of course, entirely harmless, 

 and are unaccompanied by u !he slightest rise of temperature, if any. 

 The only role which we can assign with any degree of probability 

 to the polynuclear leucocyte in the struggle against tubercle has 

 regard to its action on bacilli which have made their way into the 

 blood. Here the conditions are much more like those which 

 occur in our opsonin experiments, and it is quite likely that 

 opsonization and phagocytosis occur. Even this is not certain, 

 however, for we do not yet know definitely whether opsonin exists 



