ACTION ON THE TISSUES 269 



outlines become indistinct, whilst their nucleus stains faintly, 

 and ultimately loses the power of staining. The cells in the 

 centre, thus altered, gradually become fused into a homogeneous 

 substance, and this afterwards becomes somewhat granular in 

 appearance. If the central necrosis does not take place quickly, 

 then giant-cell formation may occur in the centre of the follicle, 

 this constituting one of the characteristic features of the tuber- 

 cular lesion ; or after the occurrence of caseation giant-cells may 

 be formed in the cellular tissue around. The centre of a giant- 

 cell often shows signs of degeneration, such as hyaline change 

 and vacuolation, or it may be more granular than the rest of 

 the cell. The exact mode of formation of a tubercle follicle 

 varies, however, in different tissues. 



Though there has been a considerable amount of discussion 

 as to the mode of origin of the giant-cells, we think there can 

 be little doubt that in most cases they result from enlargement 

 of single epithelioid cells, the nucleus of which undergoes pro- 

 liferation without the protoplasm dividing. These epithelioid 

 cells may sometimes be the lining cells of capillaries. Some 

 consider that the giant-cells result from a fusion of the epithelioid 

 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. 

 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, 



