198 Microscopic Histochemistry 



enzyme splits hexosediphosphate into two molecules of triose 

 phosphate. The latter hydrolyzes spontaneously at an alka- 

 line reaction, and the phosphate liberated is visualized much 

 as in the regular method for alkaline phosphatase. lodoace- 

 tate and fluoride are added to the incubating mixture to pre- 

 vent the dismutation of triose phosphate and the hydrolysis 

 of hexosediphosphate by alkaline phosphatase, respectively. 

 Frozen sections (whether fixed or unfixed, not clear from the 

 text) must be used, because paraffin sections give no re- 

 action. 



This method is open to criticism on several counts. Zymo- 

 hexase itself is quite soluble and cannot be expected to re- 

 main in situ under the conditions of the method. But the 

 main objection is this: even if it were granted that hexosedi- 

 phosphate will be attacked by only zymohexase under the 

 conditions specified (and this is certainly not true, since reg- 

 ular alkaline phosphatase hydrolyzes hexosediphosphate 

 quite readily and is not inhibited by fluoride), the second 

 step, namely, that of the spontaneous dephosphorylation of 

 triose phosphate, is far too slow to permit localization, since 

 triose phosphate is highly diffusible. There can be no doubt 

 that its decomposition will take place almost quantitatively 

 in the ambient fluid and not in the tissue. 



The illustrations given in the original paper do not corre- 

 spond to the distribution of regular alkaline phosphatase. 

 However, it is impossible to tell just what is demonstrated by 

 the method. It is quite likely that some undetermined un- 

 stable phosphatase, intolerant to embedding, is responsible 

 for the reaction. 



SULFATASE 



Extracts of plant and animal tissues hydrolyze a variety of 

 sulfuric esters, such as chondroitinsulfuric acid,^^ sulfates of 



91. Neuberg, C, and Hoffmann, E.: Biochem. Ztschr., 234:345, 1931. 



