Organic Substances 105 



The acetal linkage is slowly hydrolyzed by acids and oxi- 

 dizing agents but promptly by heavy-metal salts such as 

 HgCl2, with liberation of the corresponding aldehyde. Ac- 

 tually, plasmal has been shown to be a mixture of several 

 long-chained aldehydes, mainly stearic and palmitic, with 

 the admixture of unidentified unsaturated ones. 



Plasmal will react with all aldehyde reagents such as 

 Schiff's, phenylhydrazine, semicarbazide, naphthoic hydra- 

 zide, etc. Highly colored reaction products (with 2,4-dini- 

 trophenylhydrazine, SchifiF's reagent, or 2-hydroxy-3-naphtho- 

 ic hydrazide followed by azo-coupling^^~^^ ) can be used for 

 its histochemical identification. 



It should be mentioned, however, that plasmal is not the 

 only lipid aldehyde in the tissues. ^^^^ Substances of aldehy- 

 dic nature are formed in large amounts by the oxidation of 

 unsaturated fatty acids. ^^^^ The presence of such nonplasmal 

 aldehydes can be demonstrated (some of them at specific 

 sites; Chu)^^ even in completely fresh tissues. Their amount 

 increases and their distribution becomes more widespread 

 on storage in either formalin or water. The eflPect is probably 

 due to atmospheric oxygen, since it is especially marked in 

 sections kept in a shallow layer of fluid. Intense reactions are 

 obtained at all sites where cholesterol or phospholipids are 

 present. This is not surprising, in view of the fact that the 

 fatty acids of cholesterol esters^^ and of phopholipids^^ show 



51. Camber, B.: Nature, 163:285, 1949. 



52. Seligman, A. M., and Ashbel, R.: BuU. New England M. Center, 

 11:85, 1949. 



53. Seligman, A. M., Friedman, O. M., and Herz, J. E.: Endocrinology, 

 44:584, 1949. 



54. Cain, A. J.: Quart. J. Micr. Sc, 90:75, 1949. 



55. Danielli, J. F.: Quart. J. Micr. Sc, 90:67, 1949. 



56. Hayes, E. R.: Stain Technol., 24:19, 1949. 



57. Chu, C. H. U.: J. Nat. Cancer Inst, 10:1344, 1950; Chu, C. H. U.: 

 Anat Rec, 108:723, 1950. 



58. Kelsey, F. E., and Longenecker, H. E.: J. Biol. Chem., 139:727, 

 1941. 



59. Page, I. H., and Rudy, H.: Ztschr. f. Physiol. Chem., 205:115, 1932, 



