300 A MANUAL OF BACTERIOLOGY 



The conception of tuberculosis was originally a purely 

 anatomical one, the name being given to a condition in 

 which the organs were studded with little yellowish points 

 or nodules, which were termed tubercles. Laennec was 

 the first to indicate the characters of these nodules or 

 tubercles, and traced with considerable accuracy their 

 development from minute lesions, 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 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 

 IX. 6). They are of the nature of plasmodia, similar to 

 the masses of fused cells which surround a foreign body in 

 the lower animals (Adami). Around the giant- cells are 

 well-defined epithelial- like cells with large and distinct 

 nuclei, which are 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 lymphoid tissue. This is the structure of a 

 typical tubercle, but one or other of the components may 

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

 teristic of the tubercle. The nodule possesses no 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. More or less extensive inflammatory 

 reaction ensues in the tissues surrounding the tubercle, 

 and the cellular elements so produced often become spindle- 

 shaped and ultimately fibrous, so that the tuberculous 

 nodule becomes enclosed by a capsule of fibrous tissue 

 which may contract and convert it into a fibrous nodule. 



