126 Microscopic Histochemistry 



pound, cannot be accepted. Pteridine derivatives do not give 

 a single one of the reactions of the EC cells in the Coujard 

 experiment. 



For the histochemical staining of the EC cells the argentaf- 

 fin reaction, azo-coupling, and the indophenol reaction are 

 recommended. With all techniques, prompt fixation of the 

 tissue is important because the EC substance undergoes 

 fairly rapid decomposition. 



The reactions are quite intense with normal EC cells; in 

 carcinoid tumors the intensity of staining is variable and may 

 even be negative, depending on the degree of biochemical 

 differentiation of the neoplastic cells. 



1 ) The argentaffin reaction.— 



i 



Method 



Fix tissues preferably in Bouin's fluid or in formalin. Other 

 formalin-containing mixtures are also usable, but the con- 

 trast between the granules, and the background is impaired 

 by dichromates and mercury salts. 



Treat sections for 10-60 minutes with Lugol's solution; de- 

 colorize with thiosulfate. This treatment helps to suppress 

 the staining of the background. Wash slides thoroughly in 

 distilled water. Incubate them for 12-24 hours at 37° C. 

 either in methenamine-silver (p. 60), buffered at pH 8-8.5 

 with a borate buffer, or in Fontana's"^ solution (p. 60). In- 

 spect the slides under the microscope at intervals; as soon as 

 the EC cells appear black, remove them from the solution. 

 Sections stained with methenamine-silver can be toned with 

 gold chloride; gold toning is not advisable after Fontana s 

 solution because it may cause considerable fading of the 

 granules. Rinse sections in a dilute solution of Na thiosulfate, 

 wash them under the tap, counterstain as desired, dehydrate, 



and mount. 



The specificity of the method is satisfactory but, like that 

 of all silver techniques, relative. On continued incubation 



29. Fontana, A.: Dermat. Ztschr., 46:291, 1925-26. 



