272 BACTERIOLOGY. 



cular focus there is formed a fibrous capsule which may 

 completely cut off the diseased from the healthy tissue 

 surrounding it. Or a tubercular focus may, through 

 the resistance of the tissue in which it is located, be 

 more or less completely isolated. In this condition 

 the diseased foci may lie dormant for a long time and 

 give no evidence of their existence, until by some in- 

 tercurrent interference they are caused to break through 

 their envelopes. With the passage of the bacilli or their 

 spores from the central foci into the vascular or lym- 

 phatic circulation the disease may then become general. 



It is to some such accident as this that the sudden 

 appearance of general tubercular infection in subjects 

 supposed to have recovered from the primary local 

 manifestations may often be attributed. The breaking- 

 down of old caseous lymphatic glands is a common 

 example of this condition. 



PRIMARY INFECTION. The primary infection occurs 

 through either the vascular or lymphatic circulation. 

 Through these channels the bacilli gain access to the 

 tissues and become lodged in the finer capillary ramifi- 

 cations or in the more minute lymph-spaces. Here 

 they find conditions favorable to their development, and 

 in the course of their life processes produce substances of 

 a chemical nature which act directly in bringing about the 

 death of the tissues in their immediate neighborhood. 

 This tissue-death is probably the very first effect of the 

 bacilli in the body, and represents the necrotic centre, 

 which can always be seen in even the most minute 

 tubercles. With the production of this progressive 

 necrosis for progressive it is, as it continues as long 

 as the bacilli live and continue to produce their poison- 

 ous products there is in addition a reactive change in 



