ACTION ON THE TISSUES 243 



cells ; but, though there are occasionally appearances which 

 indicate such a mode of formation, it cannot be regarded as of 

 common occurrence. In some cases of acute tuberculosis, when 

 the bacilli become lodged in a capillary the endothelial cells of 

 its wall may proliferate, and thus a ring of nuclei may be seen 

 round a small central thrombus. Such an occurrence gives rise 

 to an appearance closely resembling a typical giant -cell. 

 According to the view here stated, both the epithelioid and the 

 giant-cells are of connective tissue origin ; and we can see no 

 sufficient evidence for the view held by some observers, chiefly 

 of the French school, that they are formed from leucocytes 

 which have emigrated from the capillaries. 



There can be no doubt that the cell necrosis and subsequent 

 caseation depend upon the products of the bacilli, and are not due 

 to the fact that the tubercle nodule is non- vascular. This non- 

 vascularity itself is to be explained by the circumstance that 

 young capillaries cannot grow into a part where tubercle bacilli 

 are active, and that the already existing capillaries become 

 thrombosed, owing to the action of the bacillary products on 

 their walls, and ultimately disappear. At the periphery of 

 tubercular lesions there may be considerable vascularity and new 

 formation of capillaries. 



The general symptoms of tuberculosis pyrexia, perspiration, 

 wasting, etc., are to be ascribed to the absorption and distribution 

 throughout the system of the toxic products of the bacilli ; in 

 the case of phthisical cavities and like conditions where other 

 bacteria are present, the toxins of the latter also play an im- 

 portant part. The occurrence of waxy change in the organs is 

 believed by some to be chiefly due to the products of other, 

 especially pyogenic, organisms, secondarily present in the tuber- 

 cular lesions. This matter, however, requires further elucidation. 



Presence and Distribution of the Bacilli. A few facts may be 

 stated regarding the presence of bacilli, and the numbers in 

 which they are likely to be found in tubercular lesions. On the 

 one hand, they may be very few in number and difficult to find, 

 and on the other hand, they may be present in very large 

 numbers, sometimes forming masses which are easily visible under 

 the low power of the microscope. 



They are usually very few in number in chronic lesions, 

 whether these are tubercle nodules with much connective tissue 

 formation or old caseous collections. In caseous material one 

 can sometimes see a few bacilli faintly stained, along with very 

 minute unequally stained granular points, some of which may 

 possibly be spores of the bacilli. Whether they are spores or 



