242 THE INFECTIOUS DISEASES. 



Such a localized tuberculosis may retain throughout the characters 

 of a local inflammation, or it may be accompanied by the clinical 

 evidences of systemic infection. It may give rise through metastasis 

 to the successive development of tuberculous inflammations in other 

 parts of the body, or to a sudden development of small foci of tubercu- 

 lous inflammation in many parts of the body at the same time general 

 miliary tuberculosis. 



A general infection may occur by the diffusion through the body of 

 bacilli derived from a local tuberculosis, such as tuberculous phlebitis or 

 arteritis, tuberculous inflammation of the thoracic duct, or from the 

 breaking into a vessel of a tuberculous lymph node. It is probably 

 seldom that a sufficient number of tubercle bacilli enter the blood chan- 

 nels at once to account for the enormous number of tubercles which are 

 sometimes found in acute general miliary tuberculosis ; but it is not un- 

 likely that from the earliest formed tubercles which develop in the walls 

 of the smaller blood-vessels new distributions of bacilli may speedily 

 take place.' 



In many cases, however, the lesion is not focal or circumscribed but 

 diffuse, and more or less widely infiltrates or replaces the tissues in- 

 volved. This is called diffuse tuberculous inflammation. 



Miliary Tubercles, Miliary tubercles are small nodules of irregular 

 shapes (Plates IV., VI. , and VII.), the smallest hardly visible to the 

 naked eye. The smaller tubercles are gray and translucent ; the larger 

 are usually, especially in the central parts, opaque and white or yellow 

 on account of the necrosis which is apt to commence here. 



In studying the reaction of the living tissues to the tubercle bacillus 

 it should be always borne in mind that while, as a whole, the lesions 

 produced are quite characteristic, there is still no one structural feature 

 or combination of features of tubercles or tuberculous inflammation which 

 is absolutely distinctive of the action of this bacillus. In doubtful cases 

 the demonstration of the presence of the germ itself may be necessary for 

 the establishment of the character of the lesion. 2 



The experimental studies in animals, as well as the morphological 

 data gathered from the examination of tuberculosis in man, show that 



applied to tubercles which are very much larger as well as to those which are very 

 much smaller than millet seeds. It is convenient, to designate a small mass of new 

 tissue formed under the influence of the tubercle bacillus, whatever its minute struc- 

 ture, as a tubercle granulum (see Fig. 112). Very frequently two or more tubercle 

 granula are joined together by a more diffuse formation of tubercle tissue to form larger 

 or smaller miliary tubercles conglomerate tubercles (see Fig. 113). 



1 It is well in the endeavor to understand the occurrence of general miliary tuber- 

 culosis or of the less striking instances of distribution of the bacilli that two varying 

 factors are constantly active and significant ; first, the virulence of the bacilli, which may 

 be slight or extreme; and, second, the vulnerability of the infected individual i.e., his 

 " predisposition " which also may be slight or extreme. Thus the distribution of 

 bacilli, be these few or many, from an infective focus, may be in different individuals 

 or at different times in the same individual of quite different significance. 



For a critical resume of the etiology and mode of origin of miliary tubercles, with 

 bibliography, see Senda, in Lubarsch and Ostertag's "Ergebnisse," Jahrgang v., p. 447. 



2 The term tubercle tissue, which is in common use, indicates a tissue formed under 

 the influence of the tubercle bacillus rather than a tissue which is morphologically chra- 

 acteristic of tuberculosis in distinction from other forms of new tissue. 



