ACTION ON THE TISSUES. 235 



and somewhat hyaline, their 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 very quickly, 

 then giant-cell formation may occur in the centre, this con- 

 stituting one of the characteristic features of the tubercular 

 lesion. The giant cells in tubercle are large, rounded, or 

 oval protoplasmic masses, often with numerous processes, 

 and containing a varying number of oval nuclei somewhat 

 poor in chromatin, which are often arranged in a ring 

 towards the periphery, sometimes collected in a clump 

 towards one end, and sometimes lying irregularly. 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 dis- 

 cussion 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 proliferation without the protoplasm dividing. 

 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 suggest 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. 



Giant cells are found especially when the caseous change 

 is relatively not very active that is, in circumstances where 

 the formative processes have time to come into play. If 

 the centre of the nodule becomes caseous, giant cells may 



