ACTION ON THE TISSUES. 245 



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 tubercular lesion, or after the occurrence of caseatiort 

 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. 



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. Sometimes 

 cells a little larger than epithelioid cells may be seen, which 

 contain only two or three nuclei ; these may be young giant-cells. 

 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 be 

 formed 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, we think, from a careful study of the 

 tubercular lesions, 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 



