CHAPTER XXIX. 



TUBERCULOSIS (CONTINUED) HISTOPATHOLOGY AND MORBID 

 ANATOMY IN MAN AND ANIMALS. 



The Tubercles. The characteristic anatomical lesion of tubercu- 

 losis is the small, avascular, nodular mass of granulation tissue, called 

 the tubercle, which has a very pronounced tendency soon to undergo 

 retrograde, degenerative changes. The formation of the tubercle 

 can best be studied experimentally, as has been done by a number 

 of investigators, including Cohnheim, Baumgarten, and others. It 

 is accomplished by injecting finely divided tubercular material or 

 tubercle bacilli from a pure culture which has been rubbed up and 

 diluted with physiologic salt solution into the anterior chamber of 

 the eye of a rabbit. Small, grayish-white, first perfectly translucent 

 nodules develop in the eye, within twelve to fifteen days. Their size 

 when first seen is perhaps not larger than a pinhead, becoming larger 

 during the next few days and at the same time less translucent; in 

 fact, their centres become opaque. Neighboring nodules become 

 confluent and in this manner larger grayish-white or yellowish-opaque 

 nodules are formed. When infected tissues are obtained from a 

 series of animals from day to day and properly fixed, embedded, 

 sectioned, and stained, for microscopic study, they show first a 

 slow multiplication of the injected tubercle bacilli. These, or rather 

 their metabolic products or endotoxins, cause some of the ordinary 

 fixed connective-tissue cells and some lymphatic endothelial cells to 

 proliferate much more rapidly than they do under normal conditions. 

 This increased rate of cell multiplication or proliferation is indicated 

 by the presence of a considerable number of karyokinetic figures. 



The new cells formed under the stimulus of the infection with 

 tubercle bacilli become larger than the ordinary connective-tissue 

 cells in normal adult connective tissue. They possess a vesicular 

 nucleus and a rather large, round, or polygonal body of protoplasm. 

 They are, in other words, the cells generally known in histopathology 

 as epithelioid cells. A number of investigators claim that the first 

 effect of the presence and multiplication of tubercle bacilli in connec- 

 tive tissue is the cell proliferation just described. Others hold that the 

 very first effect is a coagulation necrosis of the connective-tissue cell 

 in the closest proximity to the multiplying tubercle bacilli, that this 

 necrosis leads to a moderate transudate with the migration of leuko- 

 cytes, and that the proliferation of the fixed connective-tissue cells 

 begins only after this has occurred. It appears that the preponderance 



