BY DR. BURDON-SANDERSON. 293 



SUPPLEMENT. 

 ABSORPTION BY THE VEINS AND LYMPHATICS. 



Under this head, certain experiments will be referred to re- 

 lating to the mode in which soluble and insoluble substances 

 find their way into the vascular system from the tissues. This 

 kind of absorption may be termed, in order to distinguish it 

 from that which takes place at the cutaneous and mucous sur- 

 faces, internal absorption. The other kind will be dealt with 

 in succeeding Chapters. 



It is obvious, so far as relates to the bloodvessels, that con- 

 sidering that the whole vascular system, with the exception of 

 that of the spleen, the medulla of bone, and some other smaller 

 tissues, is lined with a continuous membrane, no substance can 

 enter them excepting in a state of solution, and consequently 

 that the process of venous absorption is one of filtration or 

 diffusion; and that, of these two, the former is excluded by the 

 fact that the pressure inside of the vascular system is every- 

 where greater than the pressure outside. As regards the lym- 

 phatic system, on the other hand, the anatomical facts des- 

 cribed in Chap. YIII. will show that there is no obstacle to the 

 entry of solid substances, provided that they are in a state of 

 extremely fine division ; so that we are led to infer that, 

 whereas it is the function of the bloodvessels to absorb sub- 

 stances which are soluble and diffusible, those which are inca- 

 pable of diffusion are taken up by the lymphatics. 



From experiments we learn, not merely that this inference 

 is correct, but that the process of absorption from the tissues 

 by the veins is, like the analogous process of secretion (Chap. 

 XXXVI.), dependent on the nervous sj'stem. 



83. Proof that Solid Matters in a State of Extremely 

 Fine Division are Absorbed from the Tissues by the 

 Lymphatics. In Chapter VIII. it has been shown that, 

 without reference to the oi'igin of the lacteals from the mucous 

 membrane of the intestine, or to the stomata, by which the 

 lymphatic system communicates with the serous cavities, the 

 absorbent system originates from those forms of interstitial 

 tissue which for the present we designate lymphatic, the char- 

 acteristic of which is that they consist of ground substance, 

 riddled in all directions by cavities containing protoplasm 

 masses i. e., cells, these cavities being in communication with 

 each other, as well as with the lymphatic capillaries, by a net- 

 work of channels (lymphatic canaliculi or Saftkandlcheii). 

 The distribution in the body of interstitial tissue having these 

 characters has not yet been sufficiently investigated ; for it is 

 only during the last year or two that its anatomical relations 

 have been more or less complete!}' made out. We already 



