308 THE DIGESTIVE ORGANS. 



seen. Instead of the double knife the freezing microtome may be used 

 and the method continued as stated (Rothe). 



The reticular fibers are seen under more favorable conditions by 

 using the following method, recommended by Oppel (91): Fresh pieces 

 of tissue fixed in alcohol are placed for twenty-four hours in a 0.5% aque- 

 ous solution of yellow chromate of potassium (larger pieces in stronger 

 solutions up to 5%), then washed with a very dilute solution of nitrate of 

 silver (a few drops of a 0.75% solution to 30 c.c. distilled water), and 

 transferred to a 0.75% solution of silver nitrate. In twenty-four hours 

 the intralobular network surrounding the blood capillaries will have be- 

 come stained. The best areas lie at the periphery of the specimen, and 

 extend about i mm. into the parenchyma. Free-hand sections are 

 made, or the specimens are quickly imbedded in celloidin or paraffin, 

 to be cut afterward by means of the microtome. The same results are 

 obtained by placing small fresh pieces of the tissue for two or three days 

 in a 0.5% chromic acid solution and then one or two days in a 0.5% 

 solution of silver nitrate. The further treatment is as in the preceding 

 method. 



The method of F. P. Mall is also employed in the examination of the 

 hepatic connective tissue. 



The following method is recommended by Berkley for demon- 

 strating the nerves of the liver : Small pieces of liver tissue from 0.5 to i 

 mm. in breadth are placed in a half-saturated aqueous solution of picric acid 

 for from fifteen to thirty minutes, and then in 100 c.c. of potassium bi- 

 chromate solution that has. been saturated in the sunlight and to which 16 

 c.c. of 2% osmic acid has been added. The specimens now remain in 

 this fluid for forty-eight hours in a dark place, and at a temperature of 

 25 C. After this the tissue is treated with a 0.25% to 0.75% aqueous 

 solution of silver nitrate for five or six days, washed (quick imbedding 

 may be employed), cut, cleared in oil of bergamot, and mounted in 

 xylol- Canada balsam. 



The cellular elements of the pancreas may be examined without 

 further manipulation in very thin lobules from the rabbit (Kiihne and Lea) . 



There are various methods of differentiating the inner and 

 outer zones of the cells. In sections of the tissue fixed in alcohol, car- 

 min stains the outer zone of the cells more intensely than the inner (R. 

 Heidenhain, 83). For the staining of the inner zone, fixation in Flem- 

 ming's fluid is to be recommended, then staining with safranin, and finally 

 washing in an alcoholic solution of picric acid. The granules of the 

 inner zone (zymogen granules) appear red. These also stain red with 

 the Biondi-Ehrlich mixture. The simplest and most precise method of 

 demonstrating the zymogen granules is that of Altmann. The secretory 

 and excretory ducts of the pancreas are shown, as in the case of the 

 salivary glands, by the chrome -silver method. 



