28 E. A. Schäfer, 



Methods of preparation. 



The animals were killed a certain time after liaving been fed 

 witli a meal consisting either of fat alone, or of meat, or of bread 

 and milk, or of bread alone. Frogs were killed from a few liours to 

 a few days after feeding; mammals (cliiefly rats, as being particularly 

 well adapted for tlie investigation) from tliree to five liours. The 

 abdomen is quickly opened, and a piece of intestiae being chosen 

 which is füll of chyme, small morseis of the mucous membrane are 

 snipped off, without washing, and at once placed in the fluid in which 

 tliey are to be fixed, and afterwards either hardened for sections or 

 macerated for teasiug. The fluids employed for fixing and hardening 

 the tissue are (1) one per cent Solution of osmic acid — (2) a mixture 

 of this with alcohol — (3) a one-flfth per cent Solution of chromic 

 acid, mixed with osmic acid in variable proportion — (4) absolute 

 alcohol. For maceration with a view to Separation of the tissue 

 elements, a mixture of glycerine, alcohol and water in equal parts 

 is employed, after the cells have been fixed and stained by a few 

 hours immersion in one per cent Solution of osmic acid; or the fresh 

 tissue is placed in a one-twentieth per cent Solution of chromic acid, 

 made with normal salt-solution instead of water, with or without the 

 addition of a little osmic acid. After forty eight hours maceration 

 the tissue Clements are easily isolated in large numbers, by simply 

 tapping upon the coverglass after they haye been partially separated 

 by teasing with needles. 



For the preparation of sections. either the freezing method has 

 been adopted, or the pieces of tissue (sometimes after further staining 

 with haematoxylin) have been dehydrated with absolute alcohol, and 

 after being passed through turpentine, have been soaked with paraf- 

 fin, cut with a microtome and the sections mounted, by the creosote- 

 shellac method, in Canada baisam. 



Lastly the tissue was in many instances examined fresh, after 

 being rapidly teased in salt-solution or serum. 



