STRUCTURE OF ABSORBENT GLANDULE. 



517 



teries and Lymphatics to perform in the function of Nutrition, is quite inconsistent with 

 what is now known of the nalfcre of that process: for, as will subsequently appear, it en- 

 tirely consists in a reaction between the tissues and the nutritious fluid, in which the vessels 

 have no share save as the channels of supply. When these channels are obstructed, or the 

 supply of new matter is cut off in any other way, the removal of the old by interstitial ab- 

 sorption becomes evident ; and that this is accomplished at least as much by the veins as by 

 the lymphatics, appears from the fact that in some tissues, in which it may take place with 

 rapidity, lymphatics do not exist. 



3. Of the Elaboration of the Nutrient Materials. 



682. The alimentary substances, taken up by the Absorbent vessels, seem 

 very far from being capable of immediate application to the nutrition of the 

 body; for we find that they are not conveyed by any means directly into the 

 Circulating current, but that they first traverse a long series of tubes, convo- 

 luted at intervals into ganglia or knots ;* and that, in the course of this pas- 

 sage, they undergo considerable changes, which tend to bring the fluid into 

 closer relationship with the Blood. It seems probable that the materials, 

 which are directly received into the Blood-vessels, are equally far from being 

 immediately applicable to the Nutritive processes ; for we find, in connection 

 with the vascular system, certain bodies having the essential structure of 

 glands, but destitute of efferent ducts ; which must restore to the circulating 

 current any substances which they withdraw from it; and which there are 

 various reasons (as will presently appear) for placing in the same category 

 with the glandulae of the Absorbent system. The Absorbent Glandulae, whe- 

 ther placed upon the Lacteals in the Mesentery, or upon the Lymphatics in 

 various parts of the body, have the same general structure. They are made 

 up of convoluted knots of absorbent vessels, the simple cylindrical canals of 

 which, however, are usually dilated into larger cavities, or cells ; and amongst 

 these, capillary blood-vessels are minutely distributed. These blood-vessels 

 have no direct communication with the interior of the absorbents and the 

 cavities of the glandulae, being separated from them by the membranous walls 

 of both sets of tubes ; but there can be no doubt that transudation readily 

 takes place from one set of canals to the other. The epithelium, which 

 lines the absorbent vessel, undergoes a marked change where the vessel en- 

 ters the gland ; and becomes more like that of the proper glandular follicles 

 in its character. Instead of being flat and scale-like, and forming a single 

 layer in close apposition with the basement-membrane, as it does in the ab- 

 sorbents previous to their entrance into the gland and after their emergence 

 from it, we find it composed of numerous layers of spherical nucleated cells, 

 of which the superficial ones are easily detached, and appear to be identical 



Fig. 207. 



Fig. 208. 



Diagram of a lymphatic gland, showing the 

 intra-glandular network, and the transition 

 from the scale-like epithelia of the extra-glan- 

 dular lymphatics, to the nucleated cells of the 

 intra-glandular. 



Portion of intra-glandular lymphatic, 

 showing along the lower edge the thick- 

 ness of the germinal membrane, and upon 

 it, the thick layer of glandular epithelial 

 cells. 



* In Reptiles, in which there are no glands or ganglia in the Absorbent system, the tubes 

 are immensely extended in length. 

 44 



