CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 517 



the whole small size. Lastly the rounded mass thus constituted 

 is surrounded by a lymph -sinus, the fluid of which on the one hand 

 bathes the mass and on the other hand is free to pass away into 

 the neighbouring lymphatic canals. As the blood streams through 

 the capillary network part of the plasma passing through the 

 capillary walls becomes lymph in the meshes of the adenoid tissue. 

 Hence, after probably acting on and being acted on by the 

 leucocytes, it passes into the lymph-sinus and so away into the 

 general lymphatic stream. In all probability the lymph-sinus is 

 chiefly filled from the fluid thus coming from the adenoid tissue, 

 so that a main current flows from the lymph-sinus into neighbour- 

 ing lymphatics in all directions ; but it may be that the lymph- 

 sinus is partly supplied by the lymphatics around, so that some of 

 the lymph from adjoining structures, while flowing in the sinus 

 around the adenoid tissue, is subjected to the action of that tissue. 

 In all probability too the transit of material from the blood to the 

 adenoid tissue is accompanied by a reverse current from the 

 adenoid tissue to the blood, so that the blood in passing through 

 the follicles not only gives but also takes. 



Since multiplication of leucocytes appears to be continually 

 going on in the adenoid tissue and since the follicles do not 

 increase indefinitely in size some of the leucocytes must disappear. 

 There is every reason to think that they pass away into the lymph- 

 sinus and so joining the general lymph stream become the 

 corpuscles of the lymph of which we shall presently speak. If the 

 central adenoid mass is, as some think, invested with a continuous 

 coat of sinuous epithelioid plates, the leucocytes which leave the 

 follicle must pass through the coat in the same manner that the 

 white corpuscles of the blood migrate through the walls of the 

 blood vessels ; but it is more probable that, as others think, the 

 coating is discontinuous, the spaces of the adenoid tissue opening 

 freely at intervals into the lymph-sinus, and thus affording an easy 

 path not only for the leucocytes but also for the fluid. 



The lenticular glands of the stomach appear to be only less 

 condensed, less completely arranged masses of adenoid tissue ; and 

 as we shall see hereafter small masses of adenoid tissue more or 

 less condensed, more or less transformed into definite follicles are 

 met with in various parts of the body. 



291. A Peyers Patch is, as the phrase "agminated gland" 

 indicates, merely an aggregation of solitary follicles. A well 

 formed Peyer's patch consists of a variable number, in man fifty 

 or even a hundred or fewer, of solitary follicles arranged in a 

 single layer close under the epithelium, but stretching down into 

 the submucous tissue, the distinction of which from the mucous 

 membrane proper is to a great extent lost by the breaking 

 up of the muscularis mucosae. Between the constituent follicles 

 glands of Lieberktihn are found encircling the follicles, and villi 

 project from the surface, while between and below the glands 



