2i6 TUBERCULOSIS. 



variety begin to appear at the periphery and gradually 

 become more numerous. 



Soon, however, the action of the bacilli as cell-poisons 

 comes into prominence, the changes first occurring in the 

 centre of the focus. The epithelioid cells become swollen 

 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 leucocytes are involved in this necrotic change their nuclei 

 generally break down into small granular particles, which 

 stain deeply and may remain visible for a considerable time. 

 If the central necrosis does not take place very quickly, then 

 giant-cell formation may occur in the centre, this constituting 

 one of the characteristic features of the tubercular lesion. 

 The giant cells in tubercle are large, rounded, or oval proto- 

 plasmic masses, often with numerous processes, and con- 

 taining 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 



