132 LYMPHATIC SYSTEM. 



however, between the outer surfaces of the cylinders and the 

 trabeculse, spaces to which we shall revert immediately. In 

 sections which have been only slightly shaken, it is possible to 

 observe that fibres stretch at more or less regular intervals 

 from the external surface of the c} r linders to the trabeculse, by 

 which the intervening space is divided into sections. These 

 fibres appear to be offsets from the trabeculre, and exhibit 

 either swellings containing nuclei, or distinct nucleated stellate 

 cells. In sections which have not been shaken, the whole me- 

 dulla^ substance appears to be uniformly full of lymph cor- 

 puscles. In the spaces, as we have seen, they can be shaken out 

 so readily, that it is evident they lie quite loosely ; whereas, in 

 the cylinders themselves, they are intimately united to the net- 

 work. The significance of this structural difference can be 

 demonstrated in glands in which the different lymphatics have 

 been injected, or, still better, in glands which have been injected 

 by the puncture method with nitrate of silver. In the former 

 case it is possible to trace the injection from the different ves- 

 sels of the cortex, through the lymph sinuses which surround 

 the follicles, to the spaces which separate the cylinders from 

 the trabeculse, and thence to the different vessels at the hilus. 

 In the latter case, lymphatic sinuses are met with in the me- 

 dullary substance near the hilus, lined with endothelium, which 

 are continuous with the spaces surrounding the cylinders in 

 such a way that their endothelium can be distinctly traced on 

 to the surface of the trabeculae. 



Solitary and Agminated Follicles of the Intestine. Folli- 

 cles such as we have just described in the cortical substance 

 of the lymphatic glands occur in the large intestine as solitary 

 follicular bodies, or in the small intestine, in groups (the so- 

 called Peyer's patches. See p. 125). 



Thymus Gland. This is to be regarded merely as an 

 aggregation of follicles of the same kind. Neither in their 

 structural elements, nor in the relation of these to the vessels 

 or lymphatics, can any difference be made out. In man, as 

 well as in the dog, the external surface of the capsules is 

 covered with an endothelium identical with that of the pleura. 

 The tonsils and follicular glands at the base of the tongue are 

 almost made up of aggregations of lymphatic follicles. 



