EXAMPLE 12 



Preparation of a Transverse Section of the Small 

 Intestine of the Frog Stained with Celestine 



Blue B-Eosine 



This is the simplest example of paraffin sectioning that can be imagined 

 and it may well serve as an introduction to this type of technique either 

 for a class or for an individual. The intestine of a frog has been selected, 

 rather than of any other animal, because of the availability of this form 

 in laboratories, but any small animal may be substituted in its place. 



Before killing the frog, it is necessary to have on hand a selected 

 fixative. Since this is intended to be an example of the utmost simplicity, 

 it is suggested that the dichromate-mercuric-formaldehyde mixture of 

 Helly (Chapter 6) be employed. This fixative is entirely foolproof be- 

 cause objects may remain in it for weeks without damage, and it also 

 permits excellent afterstaining by almost any known technique. If only 

 a piece of intestine is to be fixed, 100 ml of fixative will be sufficient. 

 There is no reason why any other organ in the animal ( with the exception 

 of the central nervous system) should not be preserved in this fluid for 

 subsequent investigation. 



The frog is killed by any convenient method, but it is usually best for 

 histological purposes to sever a large blood vessel and permit as much 

 blood as possible to drain out from the heart before opening the abdomi- 

 nal cavity and removing the intestine. One or more lengths of about % in. 

 should be cut from the intestine and then transferred directly to the 

 fixative where they may remain overnight. 



When they are next required, the specimens should be removed from 

 fixative, washed in running water for a few hours, and then transferred 

 directly to 70 per cent alcohol. The easiest method of washing objects 

 of this size in running water is to take one of the coplin jars previously 

 described, fill it with water and insert the specimen, and then attach a 

 cover of coarse cheesecloth with a rubber band. The jar is placed in the 

 sink and a narrow stream of water is permitted to fall on it from the tap. 



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