INTRODUCTION 



The chemical techniques to be described are all of the quantitative 

 variety and they differ from their macro counterparts primarily as 

 regards the volumes employed and the mode of handling them. In 

 general, the same reactions and concentrations of reagents are used 

 in both. The degree to which the localization of the chemical constit- 

 uents in tissues and cells is limited, in these techniques, largely 

 depends upon the degree to which the anatomical parts can be 

 isolated mechanically in preparation for their separate analysis. The 

 precedures most commoly used are: (a) the preparation of serial 

 microtome sections of tissue and analysis on each of selected sec- 

 tions, (fc>) isolation of cells or cellular particulates by centrifugation 

 for their separate analyses, or (c) use of micro dissection to obtain 

 the part to be analyzed. It is considerably more of a problem, as a 

 rule, to obtain a satisfactory sample for analysis than to perform 

 the analysis itself. While the ultimate goal of being able to apply 

 quantitative procedures in situ to biological material is still essen- 

 tially beyond the present horizon, the use of these chemical 

 techniques can lead to the acquisition of knowledge which can now 

 be obtained by no other means. 



It should be pointed out that in the interests of simplicity and 

 accuracy certain well-established procedures of macroquantitative 

 analysis are best avoided in work on the level considered here. The 

 procedures to be given are those of the original authors, but the 

 laboratory worker should introduce his own simplifications of the 

 following type at every opportunity : (1) Avoid quantitative trans- 

 fers — rather remove an aliquot. (2) Avoid dilution to a given volume 

 in a vessel; this necessitates the calibration and marking of the 

 vessel — rather dilute by adding a known volume of liquid with 

 a pipette. (5) Employ pipettes calibrated to deliver rather than to 

 contain — this obviates the necessity of rinsing the pipette. (4) Avoid 

 filtration when it is possible to separate a precipitate by centri- 

 fugation. 



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