28o BACTERIA 



set up by the toxins of the bacillus. Directly the invading 

 bacilli find themselves in a favourable nidus they commence 

 multiplication. In three or four days this acts as an irritant 

 upon the surrounding connective-tissue cells, which prolifer- 

 ate, and become changed into large cells known as epithelioid 

 cells. At the periphery of this collection of epithelioid cells 

 we have a congested area. This change has been accom- 

 plished by the presence of the bacilli themselves. The pro- 

 duction of their specific poisons changes the epithelioid cells 

 in the centre of the nodule, some of which become fused 

 together, whilst others expand and undergo division of 

 nucleus. By this means we obtain a series of large multi- 

 nucleated cells named giant cells. If the disease is very 

 active, these soon caseate and break down in the centre. 

 In a limb we get a discharge ; in a lung we get an expector- 

 ation. Both discharge and expectoration arise from a break- 

 ing down of the new cell formation. Previously to breaking 

 down we have in a fully developed nodule healthy tissue, 

 inflammatory zone, epithelioid cells, giant cells, containing 

 nuclei and bacilli. The sputum or the discharge will, dur- 

 ing the acute stage of the disease at all events, contain 

 countless numbers of the bacilli, which may thus be readily 

 detected, and their presence used as evidence of the disease. 

 It is obvious that if the centre of the nodule degenerates 

 and comes away as discharge a cavity will be left behind. 

 By degrees this small cavity may become a very large one, 

 as is frequently the case in the lung, which particularly 

 lends itself to such a condition. Hence, though at the out- 

 set a tubercular lung is solid, at the end it is hollow. 



The exact period of giant-cell formation depends on the 

 rapidity of the formative processes. Thus different condi- 

 tions occur. Inside the giant cells the bacilli are arranged 

 in relation to the nuclei in one of three ways: {a) polar, {p) 

 zonal, or {c) mixed. The breaking down of the nodule is 

 partly due to the cell-poisons, and partly because the nodule 



