Fluorescence 401 



Thudichum published on hematoporphrin, which he called " cruen- 

 tine." In a long (142 pp.) and little-known paper " On the Chemi- 

 cal Identification of Disease," containing beautiful plates of the 

 absorption spectrum of various biological pigments, he wrote (p. 



228): 



It [neutral cruentine] fluoresced with a splendid blood-red colour in the 

 sun-cone. This is the first body which is known to fluoresce with homo- 

 geneous light, that is to say, the same kind of light or colours which 

 it transmits. . . . Considering its beauty alone, the phenomenon may be 

 placed by the side of those exhibited by quinine, chlorophyle, or cudbear. 



The possibility of using fluorescence as a method of detecting or- 

 ganic compounds was certainly present in Stokes' mind, as he lec- 

 tured " On the application of the optical properties to detection 

 and discrimination of organic substances " before the Chemical 

 Society and the Royal Institution in 1864. The same idea was pre- 

 sented by Victor Pierre, a professor at Prague, later at the Poly- 

 technicum in Vienna, in a series of papers, beginning in 1862. 

 Pierre studied solutions of single fluorescent compounds and mix- 

 tures. He satisfied himself that fluorescent band spectra were char- 

 acteristic of a particular substance, if the same exciting light was 

 used. He noted that the spectra were different in different solvents 

 and especially stressed the effect of acidity and alkalinity. F. Goppel- 

 roder used the word " Fluoreszenzanalyse " in connection with an 

 extract of " Kubaholz " in 1868. In the twentieth century this tech- 

 nique has become a most important tool. The fluorescence-micro- 

 scope has been developed for examining cells and tissues, and fluo- 

 rescence analysis of solutions is regularly used for quantitative deter- 

 mination of compounds. 



CHEMICAL CONSTITUTION AND FLUORESCENCE 



With the rise of organic chemistry, many new synthetic substances 

 became available. Fluoresceine was prepared by A. von Baeyer in 

 1871, and eosine, a related fluoresceine dye by H. Caro in 1874. 

 These are examples of a number of organic compounds with fluoro- 

 phore groups, which have become legion. Such fluorescence colors 

 are now used for special effects in the theatre, for the production 

 of a brilliant sheen on clothing, and for advertising. The relation 

 between fluorescence, color, and chemical constitution became a 

 popular study in the 1880's, and in fact has continued to be imtil 

 the present day. In 1880 Liebermann called attention to the fact 

 that anthracenes were fluorescent, anthraquinones not, and thought 

 that numerous internal linkages were connected ^vith fluorescence 



