ORIGIN' OF THE LYMPHATICS. 



303 



It is assumed by Arnold that the blood-vessels communicate with the juice-canals, and that 

 fluid passes out of the thin-walled capillaries through their stomata into these spaces ( 65). 

 This fluid nourishes the tissues, the tissues take up the substances appropriate to each, while 

 the effete materials pass back into the spaces, and from these reach the lymphatics, which 

 ultimately discharge them into the venous blood. 



Whether the cells within these spaces are actively concerned in the pouring out of the blood- 

 plasma, or take part in its movement, is matter of conjecture. We can imagine that by con- 

 tracting their body, after it has 

 been impregnated with fluid, this 

 fluid may be propelled from space 

 to space towards the lymphatics. 

 The leucocytes wander through 

 these spaces until they pass into 

 the lymphatics. Fine particles 

 which are contained in these spaces 

 e.g., after tattooing the skin, 

 and even fatty particles after in- 

 unction are absorbed by the 

 leucocytes, and carried by them to 

 other parts of the body. [The 

 pigment particles used to tattoo the 

 finger are usually found within the 

 first lymphatic gland at the elbow.] 



The migration of cellular 

 elements from the blood-vessels 

 into the origin of the lym- 

 phatics is to be considered as 

 a normal process. Granular 

 colouring-matter passes from 

 the blood into the protoplasmic 

 body of the cells within the 



lymph-spaces ; and only when -pig. 217. 



the granular pigment is in pleural surface of the central tendon of the diaphragm of 

 large amount, does it appear the rabbit stained with silver nitrate. L, lymphatic with 

 as a Granular injection in the its sinuous endothelium; c, cells of the connective-tissue 

 brandies of the juice-spaces. brou S ht into view ^ the silver nitrate ' 



(2) Origin within villi i.e., of the chyle vessel or lacteal has been described ( 190). 



(3) Origin in perivascular spaces (fig. 218). The smallest blood-vessels of bone, the central 

 nervous system, retina and the liver, are completely surrounded by wide lymphatic tubes, so 

 that the blood-vessels are completely bathed by a lymph-stream. In the brain these lymphatics 

 are partly composed of delicate connective-tissue fibres, which traverse the lymph-space and 

 become attached to the wall of the included blood-vessel. Fig. 218, B, represents a transverse 

 section of a small blood-vessel, B, from the brain ; p is the divided perivascular space. This 

 space is called the perivascular space of His, but in addition to it the blood-vessels of the brain 

 have a lymph-space within the adventitia of the blood-vessels ( Virchow-Robin's space). It is 

 partly lined by well-defined endothelium. Where the blood-vessels begin to increase consider- 

 ably in diameter, they pass through the wall of the lymphatics, and the two vessels afterwards 

 take separate courses. In all cases, where there is a perivascular space, the passage of lymph- 

 and blood-corpuscles into the lymphatics is greatly facilitated. In the tortoise the large blood- 

 vessels are often surrounded with perivascular lymphatics. Fig. 218, A, gives a representation 

 of the aorta surrounded by a perivascular space which is visible to the unaided eye. In mam- 

 mals the perivascular spaces are microscopic. 



(4) Origin in the form of interstitial slits within organs. Within the testis the lymphatics 

 begin simply in the form of numerous slits, which occur between the coils and twists of the 

 seminal tubules. They take the form of elongated spaces bounded by the curved cylindrical 

 surfaces of the tubules. The surfaces, however, are covered with endothelium. The lymphatics 

 of the testis get independent walls after they leave the parenchyma of the organ. In many 

 other glands the gland- substance is similarly surrounded by a lymph-space. The blood-vessels 

 pour the lymph into these spaces, and from them the secreting cells obtain the materials 

 necessary for the formation of their secretion. 



(5) Origin by means of free stomata on the walls of the larger serous cavities, which (fig. 

 219, a) communicate freely with the lymphatics. The investigation of the serous surfaces is 

 most easily accomplished on the septum of the great abdominal lymph-sac of the frog. Silver 



