108 MICROSCOPIC TECHNIQUES 



Chemotherapeutics. Helander ( 1945a) has reported the detec- 

 tion of chemotherapeutics in paraffin sections prepared from frozen 

 dried tissue. The blue fluorescence of tissue itself, when illuminated 

 by ultraviolet, may obscure the fluorescence of compounds present 

 if they too have a blue fluorescence. This difficulty can be circum- 

 vented in some cases by heating the sections for a short period in 

 order to change the color of the fluorescent light emitted by the 

 drug. In a work of a high order of excellence Helander (1945b) 

 presented a table (Table I) of the fluorescences of various tissues, 

 and after intramuscular injection of drugs into mice, he found that 

 sections of muscle tissue showed the fluorescences indicated in 

 Table II. 



Fischl and Singer (1935) made use of the fluorescences of atebrin 

 and trypaflavin to show that these compounds are taken up in vivo 

 by trypanosomes. A table of the fluorescences of compounds, and of 

 certain parasites after treatment with them, has been given in a 

 paper by Bock and Oesterlin ( 1939) . 



Metals. The detection of uranium salts in incinerated sections 

 of tissue has been made possible by the fluorescence of these salts, 

 (page 145). 



The colors of the insoluble 8-hydroxyquinoline derivatives of iron, 

 calcium, magnesium, aluminum, manganese, zinc, and copper have 

 been used for identifications of these metals in tissue sections (see 

 page 21). However, no one seems to have exploited the possibility 

 of utilizing the fluorescences of these derivatives. DeMent (1942) 

 lists the fluorescent colors of 27 metallic hydroxyquinolinates, and 

 it would appear that, in some cases at least, a more clear-cut 

 differentiation between the metals would be possible on this basis. 



Spectroscopic Analysis of Fluorescence 



The identiflcation of substances in tissues by means of the spec- 

 troscopic analysis of the fluorescent light they emit has been utilized 

 to some degree. Dhere ( 1939) presented a thorough and able review 

 of this technique and gave data relative to various carbohydrates, 

 lipids, proteins and amino acids, alkaloids, chlorophylls, bile pig- 

 ments, porphyrins, carotenoids, flavins, thiochrome, and a few other 

 special compounds. Either direct vision or grating microspectro- 

 scopes may be employed, and the spectral lines of mercury can be 



