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RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



straight lines A were probably caused by scratches on the emulsion; the 

 fact that all these grains appear in the same plane of focus is suspicious. 

 Darkening due to debris B or to bubbles or dust particles C can usually be 

 recognized by the characteristic appearance. In this autoradiogram 

 there seemed to be a greater concentration of grains over the intercellular 



Fig. 7-20. Artifacts in Ca^" autoradiogram of cartilage of 9-day chick embryo. A, 

 straight lines probably caused by scratch on emulsion; B, darkening probably due to 

 debris; C, dark spot probably due to bubble or dust particle. Note greater concentra- 

 tion of grains over intercellular matrix D than over chondriocytes E. {Courtesy of 

 P. M. Johnston.) 



matrix D than over the chondriocytes E. When the autoradiographic 

 localization does not conform to some anatomical or physiological pattern, 

 then one should strongly consider the possibility of artifacts. 



Many of the uncertainties have been eliminated in the procedures that 

 have been described. However, it is always wise in making a series of 

 autoradiograms to include similar samples with no radioactivity as a con- 

 trol for errors that may tend to produce extraneous images. With gross 

 samples, it is sometimes possible to dissect out regions corresponding to 

 different areas of darkening and measure the radioactivity. 



GENERAL REFERENCES 



1. Guyer, Michael F.: "Animal Micrology," University of Chicago Press, Chicago, 

 1930. 



2. Click, David: "Techniques of Histo- and Cytochemistry," Interscience Pub- 

 lishers, Inc., New York, 1949. 



