XVIII.] THE LYMPHATIC SYSTEM. 197 



and red blood corpuscles not washed out of 

 the reticulum will be present. 



c. The reticulum of the Malpighian corpuscles 

 resembles that of the follicles of lymphatic 

 glands, in its meshes are many leucocytes, 

 but no red blood corpuscles. 



d. The small arteries, capillaries and veins of 

 the pulp; the veins branch out from the 

 trabeculae and have sharp outlines with 

 nuclei at intervals (they may usually be 

 recognized in the dog by the spiral lines 

 running round them). 



e. The trabeculas are chiefly composed of un- 

 striated muscle tissue (the amount of this 

 varies in different animals, in some it is very 

 small). 



3. Prepare a section of spleen injected 1 with Berlin 

 blue from the splenic artery under a low pressure. 



1 A dog is perhaps the best for injection, but a cat or a rat answer 

 the purpose very welL In a dog the individual arteries and veins 

 which run to the spleen are large enough to be easily injected 

 separately, and since the fluid (especially with an arterial injection) 

 does not readily spread out beyond the section of the spleen directly 

 supplied by the vessel, a number of injections may be made in the 

 same animal. The whole spleen should be washed out first from the 

 coeliac artery. To avoid clotting it is advisable to inject 10 p. c. 

 peptone into the jugular before bleeding. The best injection material 

 is a '2 p. c. solution of nitrate of silver, after the injection pieces of 

 the spleen are put in 75 p. c. alcohol for a day or two, then cut with 

 the freezing microtome and exposed to the light. The disappearance 

 of the epithelium of the capillaries and small veins of the splenic 

 pulp show in the clearest manner the opening of these into the spaces 

 of the pulp. 



