Example 10 



Preparation of a Transverse Section of the Small Intestine 

 of the Frog Stained with Celestin Blue B-eosin 



This is the simplest example of paraffin sectioning which 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 sug- 

 gested that the cupric-nitric-paranitrophenol mixture of Petrunkewitsch (see 

 p. 11) be employed. This fixative is entirely foolproof because objects may 

 remain in it for weeks without damage, and it also permits excellent after- 

 staining by almost any known technique. If only a piece of intestine is to be 

 fixed, 100 cc. 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 his- 

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

 possible to drain out from the heart before opening the abdominal cavity and 

 removing the intestine. One or more lengths of about one third of an inch 

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

 where they may remain from a few hours to several weeks. 



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

 tive, 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 

 permitted to fall on it from the tap. It will be found that the specimen will 

 swirl around in the jar in a most satisfactory manner. This simple device saves 

 all the trouble of rigging up glass tubes and boring corks to make the cum- 

 bersome apparatus sometimes recommended for the purpose. 



The actual procedure of embedding has already been described in some de- 

 tail. The specimen is transferred after 24 hours in 70 per cent alcohol to 96 per 

 cent alcohol. It is better to use a large volume of this alcohol and to suspend 

 the object in it than it is to use relatively small volumes frequently changed. 

 It is recommended, therefore, that a wide-mouthed stoppered jar of about 



110 



