Sections of skin of selachians and teleosts are fixed in 10% formalin soln., macerated in several changes of 3% KOH soln. until translucent, then stained for 24 hrs. in fresh 2% KOH soln. to which is added a sat. alcoholic soln. of alizarin red S. Destain, if necessary, in acid alcohol, dehydrate in cellosolve or alcohol, clear in methyl salicylate.