DISTRIBUTION OF THE BACILLI. 



247 



tively slow growth, but retains its forin and staining power for a 



much longer period than most organisms. This is true of the 



bacilli both in 



cultures and -^, .#*' '^*(~.'^^ 



also in the 



tissues. 



As regards 

 their position 

 in the tissues, 

 the bacilli are 

 usually scat- 

 tered irregu- 

 larly or in 

 small groups 

 amongst the 

 cells or gran- 

 ular material. 

 Most of the 

 bacilli lie free, 

 and their oc- 

 currence with- 

 in the cells is 

 relatively un- 

 common, there 



being in this respect a contrast to what is seen in the lesions in 

 leprosy. Occasionally we find them within the giant-cells, 

 in which they may be arranged in a somewhat radiate manner 

 at the periphery, occasionally also in epithelioid cells and in 

 leucocytes ; but these are by no means frequent sites in the 

 human subject. 



The above statements, however, apply only to tuberculosis 

 in the human subject, and even in this case there are exceptions. 

 In the o.x, on the other hand, the presence of tubercle bacilli 

 within giant-cells is a very common occurrence ; and it is also 

 common to find them in considerable numbers scattered irregu- 

 larly throughout the cellular connective tissue of the lesions, 

 even when there is little or no caseation present (Fig. 91). 



In tuberculosis in the horse, and in avian tuberculosis, the 

 numbers of bacilli may be enormous, even in lesions which are 

 not specially acute ; and considerable variation both in their 



Fig. 90. — Tubercle bacilli in section of human lung in acute 

 phthisis. The bacilli are seen lying singly, and also in large masses 

 to left of field. The pale background is formed by caseous material. 

 Stained with carbol-fuchsin and Bismarck-brown. X looo. 



