330 TUBERCULOSIS AS A TYPE OF BACTERIAL DISEASE 



The Relation of the Bacillus to the Disease.— Having con- 

 sidered the structure of " tubercles " and the chief biological facts of 

 the tubercle bacillus, we may now ask : How does the bacillus set up 

 the changes in normal tissues which result in tubercular nodules ? 

 In arriving at a solution of this problem, we are materially aided if 

 we bear in mind the fact that when such an organism is present 

 in the tissues it has a double effect. First, there is an ordinary 

 inflammatory irritation ; and, secondly, there is a specific change set 

 up by the toxins of the bacillus. Many authorities believe that the 

 process is, generally speaking, as follows: — Directly the invading 

 baciUi find themselves in a favourable nidus they commence multi- 

 plication. In the course of a few days this acts as an irritant upon 

 the surrounding connective-tissue cells, which proliferate, and become 

 changed into the large cells known as epithelioid cells. At the periphery 

 of this collection of epithelioid cells, we have a congested area filled 

 with lymphocytes drawn thither by the process of inflammation and 

 constituting the zone of lymphoid cells. The production of the 

 bacillary 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 multinucleated cells, giant cells. Thus is formed the typical 

 " tubercle." But if the disease is very active, this soon caseates and 

 breaks down in the centre. In a limb we get a discharge; in a 

 lung we get an expectoration. Both discharge and expectoration 

 arise from a breaking down of the new cell formation. Previously 

 to breaking down we have in a fully developed nodule commencing 

 at the periphery where the normal tissue is, healthy tissue, then the 

 inflammatory zone of lymphoid cells, then epithelioid cells, and in 

 the centre giant cells, containing nuclei and bacilli. The sputum 

 or the discharge will, during 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 a purulent discharge, a cavity will be left behind. 

 By degrees this small cavity becomes enlarged, as is freqviently the 

 case in the lung, which particularly lends itself to such a condition. 

 Hence, though at the outset the affected part of a tubercular lung 

 becomes solid, ultimately the affected part becomes a cavity, unless 

 repair sets in, and by growth of fibrous tissue the commencing cavity 

 is obliterated. 



The exact period of giant cell formation depends on the rapidity 

 of the formative inflammatory processes. Thus different conditions 

 occur. Giant cells are a constant feature of interstitial tubercles 

 in connective tissue, but in uncomplicated caseous tubercular 

 pneumonia there may not be found a single giant cell in 



