230 PRACTICAL HISTOLOGY. 



splenic artery, and the organ is then hardened in the 

 same way as before. It will much facilitate the process 

 of hardening if the salt solution is followed by a stream 

 of the bichromate. This may even be made to distend 

 the organ somewhat, the distension being maintained by 

 ligaturing the vessels near the hilus. In such a case the 

 organ is to be placed entire in 2 per cent, bichromate, and 

 only cut into pieces after forty -eight hours. For a spleen 

 which has been thus prepared, the cacao-butter method 

 of embedding may be employed, after a thin piece has 

 been stained by alcoholic logwood. By thus removing 

 the blood corpuscles the retiform tissue of the pulp is 

 better seen. Klein (Quarterly Journal of Microsco- 

 pical Science, October, 1875 , relying on appearances 

 presented by preparations made in this way, describes 

 the retiform tissue of the spleen as entirely made up of 

 flattened cells forming by their junction a "honeycomb 

 of membranes." That such a description is far too ex- 

 clusive, the study of teased preparations amply demon- 

 strates, for the network of branched cells, described by 

 almost all previous observers, is readily seen in them 

 (see below, Prep. 4). 



Preparation 3. Injected spleen. The spleen 

 may have been injected in the animal which was 

 injected entire ; if this is not the case, a special in- 

 jection is to be made from the splenic artery. When 

 successfully accomplished, the vessels are as usual 

 ligatured to prevent the escape of the injection, and 

 the organ is immersed entire in spirit, at first weak 

 but with the strength afterwards gradually increased, 

 as in the case of the liver. The sections will show 

 what at first sight look like accidental extrava- 

 sations, large patches namely of injection distributed 

 all over the organ, with the exception of large round 

 white patches here and there, pervaded by a few 

 capillaries. The white patches are sections of the 

 Malpighian corpuscles, and the part permeated by 

 the injection is of course tbe pulp, into which the 

 arterial capillaries freely open. 



Preparation 4. Splenic cells. To obtain 

 specimens of the spleen substance, which will show 



