EMISSION HISTOSPECTROSCOPY 109 



used conveniently for calibration after the filters are removed, since 

 a mercury arc is the source of the radiation. 



More recently Sjostrand (1946a,b) has employed this technique 

 for the localization of riboflavin and thiamine in cells. Sjostrand 

 used the freezing-drying treatment on this tissue (frog eyes, etc.) 

 followed by paraffin infiltration. The 3-5 [x sections were subjected 

 to ultraviolet illumination on the stage of a microscope and the 

 fluorescent light which resulted was passed from the ocular into a 

 spectroscope for analysis. 



B. EMISSION HISTOSPECTROSCOPY 



The technique for the identification of certain elements in selected 

 histologically defined portions of tissue by means of emission spectra 

 was developed independently and at about the same time by Gerlach 

 and Gerlach, and by Policard. Modifications were made later chiefly 

 by Scott and Williams. The emission spectra are obtained from the 

 radiation produced by consuming, in high-frequency spark, a chosen 

 cellular region of a tissue section or a selected bit of biological 

 material. The amount of tissue destroyed in sections is a disc of 

 about 1 mm. diameter and 0.1 mm. depth; this would have a weight 

 of approximately 0.08 mg. and hence elements giving good spectral 

 lines can be detected in this quantity of fresh or fixed tissue. Ele- 

 ments that have been identified by this technique include potassium, 

 sodium, calcium, magnesium, manganese, aluminum, iron, zinc, lead, 

 copper, mercury, silver, gold, carbon, silicon, phosphorus, and boron. 

 Attempts at quantitative work have been made, but the technique 

 is primarily qualitative at present. 



There is little essential difference between the apparatus developed 

 by Gerlach and Gerlach (1933) and Policard (1931-1932, 1933a). 

 The former employed a high-frequency generator that was superior 

 to the one used by Policard, and the latter used a metal slide to hold 

 the tissue section instead of the glass slide used by the Gerlachs. 



1. Policard Technique 



A frozen section, 50-200 fi thick, cut preferably from fresh tissue 

 or else from alcohol or formalin-fixed material, is placed on a slide 

 of pure platinum or gold which is fastened to the microscope stage 



