ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 503 



the liver-cells, a dog was fed for two days on boiled potatoes to which fat 

 had been added to make them tasty. The animal was then killed, and 

 pieces of the still warm liver were cut with a freezing microtome. The 

 sections were placed in iodized serum and immediately examined. Glycogen 

 was found by this method to be disposed diffusely in the liver-cells, the 

 contents of which had assumed a brown colour. At first the glycogen 

 collects in small irregular masses, but afterwards appears on the cell-surface 

 as lumps stained by the iodine. In sections exposed for some minutes to 

 the vapour of osmic acid the glycogen is fixed within or without the liver- 

 cells without taking on the characteristic wine-red iodine reaction. This 

 staining of the glycogen is unfortunately not permanent, for it begins to 

 disappear in 24 to 48 hours. After leaving the sections in iodized serum 

 for 24 hours, no more glycogen is found. 



As an injection mass for the liver vessels Eanvier used gelatin and 

 Prussian blue (gelatin, 1*0; prussian blue, 25 -O); and also carmin. The 

 gelatin is softened in water, and all the water not imbibed is poured off. 

 It is then dissolved in a water-bath, and to it is added a carmin solution 

 prepared as follows : — Over some carmin No. 40 is poured water sufficient 

 to saturate it. When after standing some hours it has assumed a pappy 

 consistence, ammonia is added drop by drop until the carmin is dissolved. 

 So much of this carmin solution (a very small quantity) is added to the 

 gelatin as will give it the required colour. This mixture is then neutralized 

 by the addition of some drops of acetic acid (1 : 2 or 3 parts water). 

 Neutralization is shown by the appearance of the wine-red colour. The 

 mass is then filtered through flannel into the injection syringe. (If the 

 temperature of the animal amounts to 36°, there is no diffusion of the 

 injection mass through the vessels, on account of the large quantity of 

 the gelatin.) After cooling, the liver is cut into small pieces of 1 cm. 

 breadth and placed for 24 hours in ordinary spirit. This suffices to render 

 the pieces of liver sectionable. 



In order to examine the intercellvilar substance of the epithelium, the 

 author used the silver method. He exposed the portal vein of a rat just 

 before its entrance into the liver, and in order to remove the blood, injected 

 through a syringe with a silver needle first distilled water, and then after 

 some seconds a silver solution (3 : 1000). The liver was then placed in 

 distilled water for one or two hours, and afterwards in spirit. On the 

 second day sections were made, mounted in glycerin, and exposed to day- 

 light. After some days they turned brown, and the intercellular spaces 

 became visible. 



Prof. Eanvier demonstrates the interlobular connective tissue by harden- 

 ing pieces of liver in alcohol and staining the sections with hsematoxylin 

 and picrocarmin. Preparations of the latter were preserved in glycerin to 

 which formic acid was added. 



The bile-ducts were injected with Hering's apparatus. With this a 

 mercurial column of 30-40 mm. is advantageous, as with higher pressure 

 slight lacerations of the biliary capillaries occur. The injection mass is 

 prepared by mixing a concentrated solution of the persulphate of iron with 

 a solution of the yellow prussiate of potash. An insoluble precipitate of 

 Prussian blue is obtained, but when moistened with water it gradually 

 becomes soluble. A too strong solution should not be used, as it easily 

 precipitates. The injection should be carried out as quickly as possible, 

 and at a low but constant pressure, 40 mm. The animals (rats, guinea 

 pigs, and rabbits) are killed by decapitation, and injected while the liver 

 is still warm. The injection usually only takes one minute. The sections 

 are afterwards mounted in dammar. 



