192 BACILLUS TUBERCULOSIS. 



or " epithelial " cells. This mass of proliferated cells is sur- 

 rounded by a zone of leucocytes which collect for the pur- 

 pose of attempting to stay and limit the infection. The entire 

 mass of cells constitutes a tubercle, and represents a reaction 

 of the tissues to the irritation caused by the tubercle bacillus 

 and its toxins. The tubercle bacillus was given its name 

 because it is the cause of, and is always found in these tuber- 

 cles. The disease was named tubercle-osis or tuberculosis. 



The continued multiplication of the tissue-cells, together 

 with the continued secretion of the tubercle toxins and the 

 growth of the bacillus, finally deprives the cells in the centre 

 of the mass of their nutrition, so that they die from starva- 

 tion ; their death is called necrosis. Such death results in a 

 cheesy mass which is surrounded by successive zones of pro- 

 liferating cells and protecting leucocytes. Infiltration with 

 lime salts may follow, or encapsulation of the tubercular area, 

 when the disease is said to be cured. 



When the tubercle is infected with streptococci, there fol- 

 low suppuration, the formation of cavities by expulsion of the 

 broken-down material, and dissemination of the process to 

 other parts of the body. Two influences are constantly ope- 

 rative, the resistance of the tissues and the destructive action 

 of the germ and its products. Of these two processes, one or 

 the other always predominates. 



Because of their resemblance to a millet-seed the small 

 tubercles are called miliary tubercles. The acute form of the 

 disease is manifested by the formation of many such small 

 growths, and is known as miliary tuberculosis. These small 

 tubercles are grayish in color, and translucent and very firm. 

 As they grow larger their centres degenerate, and they become 

 soft and yellow. Diffuse tubercle tissue may also be formed. 

 This is also composed of many cells, but does not tend to 

 remain localized, nor does it break down. 



In the acute tubercular processes the bacilli are very numer- 

 ous. In the chronic lesions they are few in number, and 

 oftentimes repeated examinations have to be made before it is 

 possible to discover the bacillus. This is especially true of 

 sputum examinations. 



Infection : By far the most frequent channel of infection is 



