Controls To Prove Validity of Technique 19 



can be tested. For instance, it can be shown that the staining 

 of beta cell granules in the pancreatic islets by chrome 

 hematoxylin^ is not due to their insulin content, since marks 

 made with commercial insulin and fixed in Bouin's fluid 

 just like a piece of pancreas do not stain. 



2. Studying the effects of fixation and embedding.— Model 

 slides (carrying, e.g., marks made with enzyme solutions) 

 can be treated with any combination of fixatives, dehydrating 

 and clearing agents, hot paraffin, etc., and the timing can 

 be varied within wide limits. The effect of these procedures 

 can be judged not only qualitatively but, to a certain extent, 

 even quantitatively ( see next chapter ) by the outcome of the 

 reaction. Such simple experiments may supplement or even 

 replace those laborious studies in which tissue blocks are 

 used and enzymatic activity, after various treatments, is de- 

 termined chemically, by test-tube methods. 



3. Quantitation of histochemical methods.— The important 

 problem of quantitation in histochemistry and the role of 

 model experiments in it will be discussed in the next chapter. 



3. Gomori, G.: Am. J. Path., 15:497, 1939. 



