108 Microscopic Histochemistry 



of an aldehydic character. The main points of their argu- 

 ments are as follows: 



1. It can be shown that the reaction is not due to plasmal, 

 since treatment of unfixed tissue by mercuric chloride causes 

 only a weak reaction. 



2. Phenylhydrazones of aldehydes react with diazonium 

 salts to form intensely colored formazans, while ketonic 

 phenylhydrazones, in the absence of replaceable hydrogen, 

 cannot couple with diazonium salts. This formazan reaction 

 is negative with nerve tissue, adrenal lipid, etc. 



3. Aniline and sulfanilic acid, according to Oster and Mu- 

 linos^^ and Boscott and Mandl,"^^ selectively block aldehydes. 

 The carbonyl groups in question are not blocked under the 

 conditions specified. 



4. The Angeli-Rimini test*^^ for aldehydes is negative with 



the tissues. 



The problem of hpid aldehydes versus ketones has been 

 subjected to an experimental study by Gomori.'^^ His findings 

 are as follows: 



1. It can be shown in model experiments that fluorescence 

 is a property of auto-oxidation products rather than of 

 ketosteroids. 



2. Positive carbonyl reactions can be obtained after for- 

 malin-free fixatives, such as a saturated solution of picric acid 

 in 50 per cent alcohol. Therefore, "unmasking" by formalin 

 is a superfluous assumption. 



3. Seligman's criteria for the nonaldehydic nature of lipid 

 carbonyl groups are not valid. Formazans do not form from 

 all aldehydes; for instance, periodate-treated glycogen is en- 

 tirely negative. The results of blocking experiments permit 



70. Oster, K. A., and Mulinos, M. G.: J. Pharmacol. & Exper. Therap., 

 80:132, 1944. 



71. Boscott, R. J., and Mandl, A. M.: J. Endocrinol., 6:132, 1949. 



72. Angeli, A., and Angelico, F.: Gazz. chim. ital., 34-1:50, 1904; Rimini, 

 E.: Atti reale Accad. Lincei, ser. 5, cl. di sc. fis., mat. e nat., 17-11:360, 

 1908. 



73. Gomori, G.: J. Lab. & CHn. Med., 39:649, 1952. 



