246 



THE INFECTIOUS DISEASES. 



lungs by some of the forms of acute phthisis (see page 513). The tuber- 

 cle bacillus is under certain conditions markedly pyogenic, and when it 

 rapidly develops in the air spaces of the lungs or suddenly gains access 

 to them in large quantities pus, serum, fibrin, and exfoliated or prolifer- 

 ated epithelial cells may collect in and largely fill the air spaces, and then 

 the whole new exudate and the old lung tissue may, over larger or smaller 

 areas, rapidly undergo coagulation necrosis. (Plates VIII. and X.) 



Thus in one phase of tuberculous inflammation the intensity and 

 rapidity of the local poisoning by the bacillus do not permit of the 

 formation of organized new tissue at all, but only of exudative products 



FIG. 120. EXUDATIVE FORM OF TUBERCULOUS INFLAMMATION SHOWING TUBERCLE BACILLI. 

 From the lung of a child. The size of the bacilli has been slightly exaggerated in the cut. 



which are apt soon to become necrotic (Fig. 120). Less intense degrees 

 of exudative inflammation are liable to develop in the vicinity of niiliary 

 tubercles anywhere in the body. 



Characters of the Tubercle Bacillus. 



The bacillus tuberculosis is a long, slender bacterium varying in length from 3 to 

 4 fj. (from one-quarter to one-half the diameter of a red blood cell) and in breadth from 

 0.2 to 0.5 p. It is frequently more or less curved, and the individual bacilli may cling 

 together end to end, forming threads or chains. It may occur in branching forms. ' 



The bacillus (Fig. 121) is stained with difficulty by the anilin dyes (see below), and 



1 Branching forms of the tubercle bacillus have been frequently seen, and while 

 their significance is not yet altogether clear, the tendency at this time is to separate this 

 organism with the diphtheria bacillus and the so-called streptothrix or actinomyces 

 forms into a group apart from the bacilli. Whether, as many think, they are more 

 closely allied to the moulds than to the bacteria, or whether they should be considered 

 in a class by themselves are problems still unsolved. For the present, we may wisely 

 consider the tubercle bacillus as one of the bacteria. 



For studies and bibliography on this subject, consult Schulze, Zeitschrift f. Infec- 

 tions-Krankheiten, Bd. xxxi., p. 153, 1899; and Lubarsch, ibid., p. 187. 



