STRUCTURE OF TUBERCLE 367 



anatomical one, the name being given to a condition in 

 which the organs were studded with little greyish nodules, 

 which were termed tubercles. Laennec was the first to 

 describe the characters of the tubercles, and traced with 

 considerable accuracy their development from minute 

 nodules, the miliary tubercles, up to the large cheesy 

 masses which may be met with in the glands and lungs. 



Microscopically, the structure of a young and typical 

 tubercle is generally characteristic. At the centre one or 

 more giant-cells are found large protoplasmic masses, 

 each containing ten to twenty nuclei arranged round the 

 periphery (Plate X, 6). They are of the nature of plas- 

 modia, similar to the masses of fused cells which surround 

 a foreign body in the lower animals (Adami), and are 

 endothelial in origin. The giant cells are embedded in a 

 mass of epithelial-like cells with large and distinct nuclei, 

 known as epithelioid, or more properly endothelioid, cells. 

 A zone of smaller cells with scanty protoplasm and small 

 nuclei surrounds the endothelioid cells ; they are known 

 as lymphoid cells from their likeness to the cells of lym- 

 phoid tissue. One or other of the components may be 

 wanting, and none can be said to be absolutely charac- 

 teristic of the tubercle. The nodule is devoid of blood- 

 vessels, and as its size increases by growth at the periphery 

 the central parts undergo degenerative changes, and may 

 become either structureless or hyaline, or be converted 

 into a soft yellowish material somewhat like cheese and 

 termed caseous. An ordinary tuberculous nodule is com- 

 posed of several adjacent tubercles. More or less exten- 

 sive inflammatory reaction ensues in the tissues surround- 

 ing the tuberculous nodule, and the cellular elements 

 often become spindle-shaped and ultimately fibrous, so 

 that the nodule becomes enclosed by a capsule of fibrous 

 tissue which may contract and convert it into a fibrous 

 nodule. After caseation has occurred calcification may 



