230 THE INFECTIOUS DISEASES. 



(Fig. 111). Tb^ slough may involve oiily the nodules, or it may involve 

 also the muscular and peritoneal coats and perforation may occur. 

 These ulcers also may afterward increase in size, and several of them 

 may be joined together. When the ulceration leads to perforation, peri- 

 tonitis and death are the usual result. In rare cases, however, the 

 patient recovers and the perforation is closed by adhesions. 



If the patient recover, the ulcers are covered by granulation tissue, 

 their edges become flattened, the granulation tissue becomes firmer and 



FIG. 111. ULCERATIOX OF PEYER'S PATCHES AND SOLITARY LYMPH NODULES ix TYPHOID FEVER. 



The swollen patches and nodules are necrotic except at their edges, the central portions forming a 

 ragged slough. 



denser, and this new connective tissue is gradually covered with cylin- 

 drical epithelium. 



The minute changes which take place in the development of the in- 

 testinal lesion are as follows: 



At first the blood-vessels around the yodujes are dila^gd and con- 

 gestedj while the nodu^rs are swollen and the epithelium may fall off, 

 TJjgn the nodules increase in size^ largely f^om a growtL) of new <^ttg.~"" 



This cell growth is essentially aiihyperplasia of normal elements of 

 the lymphatic tissue, namely, the lymph cells and the endothelium of the 

 trabeculse and sinuses. There are thus two main types among the new- 

 formed cells, first, small cells w^ith relatively large and deeply staining 

 nuclei; and second, larger polyhedral or rounded cells with more or 

 less vesicular nuclei. The larger cells may contain foreign substances, 

 such as red blood cells or leucocytes (Fig. 112). The occurrence of 

 mitotic figures in the endothelial cells while these are in situ, and the 

 position and grouping of the large cells appear to prove their endothelial 

 origin. The production of new cells is not confined to the nodules, but 

 extends also to the adjacent mucous membrane. In many cases also little 

 foci of similar new-formed cells are found in the muscular, subserous, and 

 serous coats. 



In this stage resolution may take place ; then the new-formed cells 

 degenerate and gradually disappear. In severer forms of the disease 

 uecrotic changes are apt to supervene, leading to the larger and small 

 ulcers above described. The factors which determine the death of the 

 hyperplastic tissues are not yet fully understood. It is believed by some 

 to be directly due to toxic substances formed by the typhoid bacilli which 



