ANATOMY OF THE LACTEAL AND LYMPHATIC VESSELS. 275 



capillaries, through what have been regarded as the stomata of these vessels. 

 These anatomical data have led to the following view with regard to the re- 

 lations between the blood, the lymph and the tissues. 



Nutrient matters are supplied to the parts by transudation through the 

 walls of the capillary blood-vessels; and the effete matters pass from the 

 lymph-spaces into the true lymphatic vessels, to be finally carried to the 

 venous system. In certain tissues and organs, however, such as the cornea 

 and fibrous membranes, the lymph -spaces or canals supply the nutrient 

 fluid ; and in the glands they probably supply part of the material used in 

 the formation of the secretions. 



In the serous membranes and in other analogous structures, there are 

 large numbers of openings into the cavities ; and the peritoneum, pleura, 

 pericardium, tunica vaginalis testis, chambers of the eye, labyrinth of the in- 

 ternal ear and subarachnoid space are to be regarded as great lymph-sacs, the 

 contained fluids being lymph, without, however, presenting the so-called 

 lymph-corpuscles. 



The relations between the blood-vessels and the smallest lymphatics are 

 very close in certain parts. In the cerebro-spinal centres, Eobin and His 

 have demonstrated a system of canals which surround the small blood-ves- 

 sels and are connected with the lymphatic-trunks or reservoirs described by 

 Fohmann and found under the pia mater. The capillary blood-vessels 

 thus float in surrounding vessels filled with liquid. These vessels surround- 

 ing the blood-vessels are called perivascular canals, and the contained liquid 

 is true lymph, containing leucocytes, or lymph-corpuscles. They exceed the 

 blood-vessels in diameter by y^Vir to ^J of an inch (20 to 62/*). Since the 

 perivascular canals of the nerve-centres have been described, similar vessels 

 have been found in the retina and in the liver. 



The true capillary lymphatics have been studied in various parts by 

 means of mercurial injections, but the presence of valves in the small trunks 

 renders it necessary to make these injections from the periphery. The ves- 

 sels have been injected in certain situations with mercury, by simply punct- 

 uring with a fine-pointed canula the parts in Avhich the plexus is supposed 

 to exist, and allowing the liquid to gently diffuse itself. Following the 

 course of the vessels, the injection passes into the larger trunks and thence 

 to the lymphatic glands. The regularity of the plexus through which the 

 liquid is first diffused and the passage of the injection through the larger 

 vessels to the glands are proof that the lymphatics have been penetrated and 

 that the appearances observed are not the result of mere infiltration in the 

 tissue. It does not appear that the vessels composing this plexus vary much 

 in size. They are quite elastic, and after distention by injection, they return 

 to a very small diameter when the fluid is allowed to escape. 



By the method above indicated, it is possible to inject the superficial 

 lymphatics of the skin, the deeper vessels situated just beneath the skin, and 

 vessels in the serous membranes, glandular organs, lungs, tendons etc., in 

 addition to the larger trunks, such as the thoracic duct. The lacteal system 

 presents essentially the same anatomical characters as the general lymphatics, 



