PREPARATION OF THE SUBSTRATES 165 



interrupted. Pieces to which coagulated blood 

 adheres, which cannot easily be removed, are rejected. 

 Finally, they are placed in a mortar and broken up 

 with a pestle, by which process the last traces of 

 blood are eliminated ; and then the connective tissue 

 can be removed. We now have a snow-white tissue, 

 which is immediately boiled. The whole process 

 takes from one to at most three hours, according to 

 the kind of tissue employed. 



The extraction of blood can also be effected by 

 thoroughly washing out the organ through the blood- 

 vessels ; but in this case, the organ must be washed 

 out again after being broken up. If the extraction 

 presents any difficulties, one can often attain one's 

 object by covering the tissue in the fresh state with 

 a very thick layer of common salt. The mixture 

 is allowed to stand for two to six hours in 

 an ice-chest; the salt is then dissolved, and 

 the washing carried on in the usual manner. 

 One must never preserve an organ from which 

 the blood has been incompletely abstracted, in 

 any particular manner, with the intention of com- 

 pleting the process later on. All preservation media 

 produce coagulation and alteration of the blood. The 

 smallest blood-vessels always contain, in that case, 

 small quantities of blood constituents. We must 

 also give particular warning against the use of bleach- 

 ing agents, as, for instance, hydrogen peroxide. The 



