CYTOCHEMICAL TESTS ON EMBRYOS 



335 



A modified Millon's reaction, devised by Serra and Lopes (1945) has been used 

 to detect the presence of tyrosine, in the protein molecule, but the color is also 

 produced by other phenolic compounds. Millons is mercuric or mercurous ni- 

 trate in nitric acid and nitrous acid. The control consists of egg albumen, gel- 

 atin and phenol. A transient color is produced by tryptophane but the tyrosine 

 color attains its maximum intensity in about 3 minutes and lasts for some months, 

 fading gradually with time. Their procedure follows: 



a. Immerse tissues in mercuric solution for 30 minutes. This is made up of 

 7. 5 gms. HgSO^; 5. 5 gms. HgCl2; and 7. gms. Na2SO^ dissolved in 85 cc. 

 of distilled water to which 12. 5 gms. of cone. H^SO^ had been added, the 

 whole being made up to 100 cc. volume with distilled water. The reaction 

 should take place in a glass stoppered bottle in water bath at 60°C. 



b. Cool the bottle in running water for 10 minutes. 



c. Add to the mercuric solution in the bottle an equal volume of distilled water. 



d. Develop the color by adding a few drops of 1 M NaNO-, (6. 9% aqueous), 

 freshly prepared. The color may last for months if the tissues are mounted 

 in glycerine. Compress cells apart beneath coverslip. 



OOCYTES OF RANA RIDIBUNDA 



Fig. 4. Tyrosine reaction, photographed without filter. 

 Fig. 5. Tyrosine reaction, photographed at higher magnification than 

 Fig. 4 and without filter. 

 *Fig. 6. Arginine reaction, photographed with green filter. Slight 



differential between cytoplasm and nucleus. 

 *Fig. 7. Same as Fig. 6 except that the nuclei have been separated from 

 the cytoplasm by compression after the arginine reaction. 



Photographs by courtesy J. A. Serra 

 ♦Figures unpublished. 



A second procedure may be used and is known as the diazo reaction for histidine 

 and tyrosine. This test gives an orange or yellow color in the presence of his- 

 tidine and tyrosine of the proteins. It is the histidine which imparts the reddish 



