THE LYMPHATIC SYSTEM. 179 



The arteries and veins of the lymphatic nodes have their 

 chief entrance at the hilus, with the efferent lymphatic vessels. 

 The main trunks divide to pass into the septa. Still finer 

 divisions pass into the reticular tissue, forming a rich capillary 

 network in the follicles and cylinders, most marked at the sur- 

 face of these bodies. In the cylinders a single axial arterial 

 branch, surrounded by a peripheral capillary system, may fur- 

 nish the supply. Another source of blood-supply may be from 

 the capsule ; small branches, both arterial and venous, which 

 ramify in its layers, send finer branches inward, encircling the 

 follicles and traversing the septa and reticulum of the lymph- 

 spaces. The capillaries possess, besides their proper wall, a 

 sheath derived from the reticulum. 



Nerves of the lymphatic nodes. Little is known on this 

 point. Nerve-fibres enter with the blood-vessels in some of 

 the larger glands of man (Kolliker), and non-medullated nerve- 

 fibres have been seen in the lymphatic nodes of the ox. Con- 

 cerning the lymphatics, they exist, as we have seen, in the 

 outer layers of the capsule, and do not differ from those in 

 other regions, forming a network in the capsule. They are 

 continuous externally with the afferent lymphatics, and inter- 

 nally with the lymph-spaces already described. 



The numerous lymphoid organs are all constructed upon a 

 plan similar to that of the nodes, in that they all represent 

 modifications in the arrangement of reticular tissue and its 

 vascular supply. 



Injection of a lymphatic gland. We may obtain an injec- 

 tion of the lymph-passages in the node by puncturing the 

 capsule with an ordinary hypodermic syringe (a method for 

 which we are indebted to Hyrtl), and injecting a mixture of 

 Prussian blue and gelatine (soluble blue, 25, solid gelatine, 1). 

 It is best to inject one of a series of connected nodes, in place, 

 exposing them by dissection in a freshly killed animal. One 

 gland is then injected from the other through the afferent and 

 efferent vessels (Ranvier). They are excised and hardened in 

 Miiller's fluid or alcohol ; sections are then made with a micro- 

 tome, after which they may be washed in water, stained for a 

 few minutes in picro-carminate of ammonia (1 per cent.), again 

 washed, and then mounted in glycerine or Canada balsam. 



Method of studying the gland substance. For the purpose 

 of demonstrating the reticulum of the lymph-spaces and the 



