362 ORIGIN OF THE LYMPH-CHANNELS. LYMPHATICS. 



system (wandering-cells). At greater or lesser distances, these secretory clefts 

 are connected with minute tubular lymphatics, which are designated lymph- 

 capillaries (Fig. 130, I, L). Their commencement results from the more intimate 

 approximation of secretory spaces (I, a). 



The lymph-capillaries, generally exceeding the capillary blood-vessels in 

 caliber, lie principally in the space midway between the arched loops of the blood- 

 capillaries (B). They are composed of delicate nucleated endothelial cells (e), 

 whose characteristic sinuous edges can be stained black by means of a solution 

 of silver nitrate. Between the endothelial cells scattered spaces, stomata, are 

 present. The endothelial cells constituting the wall are often united by bridges 

 of protoplasm. According to Kolossow, the cells may recede from one another 

 at their edges, and thus form spaces between them, while the connecting bands 

 of protoplasm are capable, subsequently, of drawing them together again. Thus, 

 the stomata would develop temporarily and again close. 



It is to be inferred that the blood-vessel system communicates with 

 the lymph-spaces ; that the blood-plasma finds its way into the lymph- 

 spaces from the thin- walled blood-capillaries through their stomata. 

 In the lymph-spaces this fluid maintains the nutrition of the tissues, 

 inasmuch as the necessary constituents are taken up independently 

 by the tissues. The materials consumed are returned to the lymph- 

 spaces and later reach the lymph-capillaries, which finally deliver them 

 to the venous system. 



To what extent the cellular elements within the lymph-spaces exert any 

 action upon the discharge of blood-plasma and later upon its propulsion into 

 the lymphatics can only be surmised. It can be conceived that, through con- 

 traction and diminution in size of their cell-bodies, as well as through partial change 

 in position from the group of secretory spaces closer to the blood-vessel to that 

 directed toward the lymph-capillary, they might exert suction upon the blood- 

 plasma transuded. If the cells, themselves, then take up the transuded fluid, 

 the conception is permissible, further, that by subsequent contraction they ex- 

 press this fluid in a certain direction, namely from secretory space to secretory 

 space, toward the lymph-capillaries. In consequence of the independent migra- 

 tion of the cellular elements through the secretory spaces into the larger lymph- 

 paths, small particles that may be contained in the secretory spaces (as, for ex- 

 ample, pigment-granules that have been rubbed into the tissue of the irritated, 

 horny skin in the process of tattooing, and also minute fat-granules, bacteria and 

 the like), and which the lymph-cells are capable of taking up through ameboid 

 movement, may be propelled onward. 



After what has been said concerning the migration of leukocytes 

 from the blood-stream through the stomata between the endothelial 

 cells of the capillaries, or through the walls of smaller vessels, the migra- 

 tion of cellular elements from the blood-vessel system into the com- 

 mencement of the lymph-channels may be regarded as a normal process. 

 Granular pigments pass from the blood into the protoplasmic bodies of 

 the cells in the lymph-spaces. Only when the granular substance is 

 present in large amount is it distributed into the ramifications of the 

 lymph-spaces as a granular injection. 



The origin of the lacteals within the villi has been outlined in their descrip- 

 tion as organs of absorption. 



Commencement of the Lymphatics in the Form of Perivascular Spaces. In 



the tissue of bony substance, of the central nervous system and of the liver, 

 the smallest blood-vessels are surrounded by wider lymph- vessels, so that the 

 blood-vessels lie in the lymph- vessels like a finger in a glove. In the brain these 

 lymph- vessels are in part constituted of delicate connective-tissue fibrils, which, 

 partly traversing the lumen of the lymph-canal, are supported upon the sur- 

 face of the blood-vessel. Fig. 130 II, B represents in transverse section a small 

 blood-vessel (B), with a peri vascular lymph-vessel, from the brain; p is the tra- 

 versed lumen of the lymph- vessel. In addition to these so-called peri vascular 

 spaces of His, the cerebral vessels are provided also with lymph-spaces within 



