172 Microscopic Histochemistry 



son, the azo dye technique is not recommended for the dem- 

 onstration of enzymes which require incubation at a pH lower 

 than 6.3. 



Esters of a- and ^-naphthol are usually so rapidly hydro- 

 lyzed that diffusion artifacts result unless the incubating mix- 

 ture is agitated all the time (p. 146). The simplest way of 

 insuring thorough agitation is to use a low-speed electric or 

 air-pressure stirrer with a long, narrow ( about /2 inch wide ) 

 strip of stainless steel as a paddle, immersed almost to the 

 bottom of the Coplin jar. Only two slides can be stained at 

 one time; one in the first and one in the fifth slot of the Coplin 

 jar; the tissues should face the stirrer. With esters of naph- 

 thol-AS which are hydrolyzed relatively slowly, stirring is 

 not necessary. 



Phosphatases 



The enzymatic hydrolysis of phosphoric esters by animal 

 tissues was first described by Grosser and Husler^ in 1912. 

 Ever since this original publication, the phosphatases have 

 attracted a tremendous amount of scientific interest, and 

 their literature has grown so vast that its mere review would 

 fill a sizable volume. 



The classification of the phosphatases is not entirely satis- 

 factory and is based partly on substrate specificity and partly 

 on pH optima. A large number of individual phosphatases 

 have been described; in some instances, however, the criteria 

 of specificity are not sufficiently clear-cut. 



It should be remarked that, by a somewhat loose usage of 

 terms, the existence of specific enzymes may be implied with- 

 out any proof. For instance, the hydrolysis of glycerophos- 

 phate in the neutral range has been reported under the title 

 of "neutral glycerophosphatase," although, in all likelihood, 

 it is due to the combined activities of nonspecific acid and 

 alkaline phosphatases, measured at a nonoptimal pH. Even 

 if such a possibihty is admitted later in the text, it would be 

 more correct to avoid the use of such ambiguous terms. There 



3. Grosser, P., and Husler, J.: Biochem. Ztschr., 39:1, 1912. 



