144 



NORMAL HISTOLOGY. 



for they are more directly exposed to the action of bacteria that may 

 gain access to the mouth. 



The reason for this vulnerability appears to lie in the close prox- 

 imity of the lymphatics to the surface and their meagre protection 

 by a thin layer of epithelium liable to abrasion or destruction. The 

 solitary follicles of the intestine, for example, are covered with a 

 single layer of columnar epithelium (Fig. 121). 



The lymphadenoid tissue of the tonsil, it is true, is protected by 

 a layer of stratified epithelium ; but the surface of the tonsil is invag- 

 inated to form the crypts of that organ, and within those crypts it 



FIG. 123. 



Section through one of the crypts of the tonsil. (Stohr.) e, stratified epithelium of the gen- 

 eral surface, continued into the crypt; /, follicles containing germinal foci. Between 

 the follicles is a more diffusely arranged lymphadenoid tissue, s, material within the 

 crypt, composed in part of lymphoid corpuscles that have wandered through the strati- 

 fied epithelium. 



is possible for bacteria to multiply and produce such an accumula- 

 tion of poisonous products as to destroy the integrity of the epithe- 

 lium and so permit an invasion of the lymphadenoid tissue beneath. 

 We therefore find the tonsils specially prone to such inflammatory 



