Quantitation in Histochemistry 25 



lines with an eyepiece micrometer. For the derivation of the 

 curve and for the possible sources of error inherent in this 

 method the reader is referred to the original paper.*^ 



It should be stressed that, with methods of the type de- 

 scribed, quantitation applies only to tissue details appearing 

 in a uniform shade, and over-all values for the entire speci- 

 men cannot be obtained. For such over-all values some 

 method like that of Doyle,^ in which the reaction products 

 are extracted from the entire section and their amount is 

 determined chemically by test-tube assay, must be used. A 

 new method,^ based on the introduction of a radioactive 

 isotope into the precipitate obtained enzymatically, also ap- 

 pears to be theoretically correct for over-all quantitation. 



With suitable minor modifications, model experiments can 

 be employed in several of the quantitative aspects of histo- 

 chemistry. 



1. The sensitivity of a method, expressed in terms of mini- 

 mal concentration of a substance still giving a recognizable 

 reaction, can be determined. 



2. The concentration of chemical constituents in tissue 

 elements can be calculated. 



3. The quantitative eflFect of procedures of fixation and 

 embedding, especially loss in enzymatic activity, can be 

 studied. 



4. The kinetics of enzymatic reactions in tissue sections 

 can be followed, and results obtained with Doyle's method 

 can be checked and supplemented. 



8. Doyle, W. L.: Science, 111:64, 1950; Doyle, W. L., Omoto, J. H., and 

 Doyle, M. E.: Exper. Cell Research, 2:20, 1951; and Doyle, W. L.: Quanti- 

 tative aspects of the histochemistry of phosphatases, in Symposium on cytol- 

 ogy (East Lansing: Michigan State College Press, 1951). 



9. Barka, T., Szalay, S., Posalaky, Z., and Kertesz, L.: Kiserletes orvostud., 

 p. 1, 1951. 



