154 PRACTICAL HISTOLOGY [XIX 



NOTES. 



Hardening after washing out. As soon as possible after the 

 animal has been killed (best by bleeding under chloroform) all 

 the branches of the coeliac artery except the splenic branches 

 are tied and warm salt solution is injected into the artery until 

 the spleen is quite pale; then 5 p.c. ammonium bichromate is 

 injected until the spleen is yellow, the splenic veins are then 

 ligatured, the spleen a little distended by further injection and 

 the arteries tied. The spleen is removed to 5 p.c. ammonium bichro- 

 mate ; in two days it is cut in pieces and left in bichromate solution 

 for a week or longer. The pieces are then placed in 30 p.c. alcohol, 

 which is renewed until it is no longer coloured ; sections may then be 

 made (best with the freezing microtome) or the pieces may be kept in 

 75 p.c. alcohol. 



Injection of blood-vessels. 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, 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 cceliac artery. 



In injecting the arteries or veins, the injection should be stopped 

 as soon as spots of injection material are seen on the surface of the 

 spleen ; if it be continued, the splenic pulp becomes more and more 

 hidden by the injection. 



The most instructive injection material is -2 p.c. solution of silver 

 nitrate ; part of the injected spleen should be cut frozen, the sections 

 shaken a little in water and exposed to light, as soon as brown specks 

 appear they should be placed in dilute alcohol, and then each section 

 transferred flat to 75 p.c. alcohol. The rest may be placed in alcohol 

 75 p.c. for one to two days, then cut frozen and exposed to light. 

 In successful specimens, the disappearance of the epithelium of the 

 capillaries and small veins of the splenic pulp shows in the clearest 

 manner the opening of these into the spaces of the pulp. 



For a spleen containing little muscular tissue, that of the rabbit 

 may be taken. The spleen of the tortoise has the capsule and 



