LOCATION' OF BACILLI IN THE TISSUES. 209 



the same way that the fat droplets of the chyle find 

 entrance into the lymphatic circulation. 



The evidence produced by Cornet points to the lungs 

 as the most common portals of natural infection for the 

 human being. Unlike most pathogenic organisms, the 

 tubercle bacillus has the property of forming spores 

 within the tissues. These spores, which are highly re- 

 sistant and are not destroyed by drying, are thrown off 

 from the lungs in the sputum of tuberculous patients in 

 large number, and unless special precautions are taken 

 to prevent it the sputum becomes dried, is ground 

 into dust and sets free in the atmosphere the spores 

 of tubercle bacilli which came with it from the lungs. 

 The frequency of pulmonary tuberculosis points lo this 

 as one of the commonest sources of infection. 



Location of the Bacilli in the Tissues. — The 

 bacilli will be found to be most numerous in those tis- 

 sues which are in the active stage of the process. 



In the very initial stage of the disease the bacilli will 

 be fewer in number than later. At this stage only here 

 and there single rods may be found ; later they will be 

 more numerous, and finally, when the process has ad- 

 vanced to a stage easily recognizable by the naked 

 eye, they will be found in the granulation zones in 

 clumps and scattered about in large numbers. 



In the central necrotic masses, which consist of cell 

 detritus, it is rare that the organisms can be demon- 

 strated microscopically. It is at the periphery of these 

 areas and in the progressing granular zone that they are 

 most frequently to be seen. 



This apparent absence of the bacilli from the central 

 necrotic area must not be taken, however, as evidence 

 that this tissue does not contain them. As bacilli, they 



