196 ELEMENTARY PHYSIOLOGY. [XVIII. 



e. Examine the splenic pulp under a high power 

 and note that the mottled appearance is due 

 to the presence of red blood corpuscles scat- 

 tered irregularly in it. 



2. Prepare a section as thin as possible of a dog's 

 spleen, from which the blood has been washed 

 out by injection with salt solution, and which 

 has subsequently been injected 1 with and then 

 preserved in ammonium bichromate 5 p. c. Stain 

 with dilute picrocarmine shake and mount in 

 glycerine. Observe under a high power. 



a. There are no distinct lymph-channels. 



b. The reticulum of the splenic pulp varies in 

 appearance in different places ; in places it 

 appears as a network of cells having in vari- 

 ous directions flange-like projections which 

 taper off and join with the similar processes 

 of neighbouring cells; elsewhere the cells 

 may be nearly or wholly absent and a reticu- 

 lum of fine fibres be seen. Some leucocytes 



1 As soon as possible after the animal has been killed (best by 

 bleeding under chloroform) all the branches of the coeliac artery ex- 

 cept the splenic branches are tied and warm salt solution is injected 

 into the artery until the spleen is quite pale; then the solution of 

 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 bichromate ; 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 micro- 

 tome) or the pieces may be kept in 75 p.c. alcohol. 



