EXAMPLE 14 



Demonstration of Spermatogenesis in the Rat Testis, 

 Using the Iron Hematoxylin Stain of Heidenhain 



The laboratory white rat is one of the best forms in which to show 

 spermatogenesis because it has a continuous breeding period, so all stages 

 are available in almost every section examined. 



The rat selected should be a young male. It can be killed most con- 

 veniently with chloroform. The scrotal sac is opened by a median incision, 

 and the testes are removed, trimming away the epididymis. The testes 

 should be placed on a clean glass plate and slashed with a sharp scalpel 

 or razor about two-thirds of the way through by cuts spaced a few milli- 

 meters apart before being thrown into the fixative solution selected. Few 

 fixatives for this purpose can surpass Allen's fluid (Chapter 6). At least 

 100 ml of fixative should be employed for a normal-sized testis, and the 

 bottle containing it should be reversed once or twice during the first few 

 hours to avoid the accumulation of diluted fluid at the bottom. The time 

 of fixation is not of any great importance but, in any case, should be over- 

 night and, in general, should not exceed a few weeks. After the object is 

 removed from the fixative, it may be washed for about an hour in running 

 water before being transferred to 70 per cent alcohol to complete the 

 removal of the picric acid. It must be emphasized that washing a speci - 

 men in water, after picric acid fixatives, results in a great de al of vacuo- 

 l ation of the cytoplasm , although this does not, in the present instance, 

 interfere with the object being studied. After three or four changes of 70 

 per cent alcohol— the testes remain in a large volume of solution for at 

 least 2 or 3 days between changes— t he final removal of the picric acid 

 may be accomplished by adding a small quantity of dry lithium carbonate 

 to the alcohol used for washing. It will be impossible to remove all the 

 yellow color, some of which is occasioned by the combination of the picric 

 acid with the albuminoids present, but the last alcohol used for washing 

 should be only very faintly tinted with yellow. It is not the color of the 

 fixed material to which objection is raised during the passage of the mate- 

 rial through paraffin; it is the fact that, unless most of the picric acid is 



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