410 MANUAL OF HISTOLOGY. 



first washed out with ^ per cent, solution of common salt until 

 the fluid from the vein is clear. Then inject y 1 ^ per cent, solu- 

 tion of osmic acid or Muller's fluid for twenty minutes. Then 

 place the spleen, in Muller's fluid for ten days, at the end of 

 this time small bits should be cut off and hardened in alcohol, 

 when it may be stained and mounted in the ordinary way. 

 The spleen of man is best prepared (E. Klein) by placing small 

 bits in a large excess of per cent, chromic acid for a week. 

 Then change it to a J per cent, solution, and in three days from 

 this to a -J per cent, solution. Finally, bits are to be placed in 

 alcohol and hardened in the usual way. 



I have obtained excellent sections, however, which answered 

 very well for demonstrations, by freezing the spleen of the 

 living cat with the ether-spray, making sections at once, and 

 staining them with Bismarck brown. In this way the retiform 

 tissue even may be seen. 



THE PANCKEAS. 



The pancreas is a compound racemose gland. It is com- 

 posed of a central duct, which sends off branches that divide 

 and subdivide until they end after the usual manner of race- 

 mose glands, by opening into collections of little vesicles or 

 acini. This mode of structure divides the gland into small 

 lobules, between which runs areolar connective tissue. The 

 same tissue envelops the whole organ. 



In each of the lobules will be found a number of acini 

 grouped around the terminal extremity of a duct. These 

 acini consist of a basement-membrane ; lining this and almost 

 filling the acinus are cubical epithelial cells. The basement- 

 membrane is composed of flat, stellate cells. Owing to their 

 branching, they do not form a completely homogeneous mem- 

 brane. The epithelial cells lining the acini are nucleated and 

 compressed closely together. Their internal portion, next the 

 lumen, is granular ; the external part is clear. This granular 

 part represents (Heidenhain) the mother-ferment, zymogen, 

 which is transformed subsequently into trypsin. It varies in 

 extent with the activity of the gland. During such activity 

 the cell is smaller and the granular part less. Between the 

 cells (Langerhaus, Saviotti) fine intercellular passages similar 



