58 STUDIES ON ALKALINE PHOSPHATASE 



activity is partly defined by the nature of the enzyme mole- 

 cules present, and partly by the spatial orientation of the 

 enzymes. 



It must be borne in mind that it is not always possible to 

 demonstrate the presence of alkaline phosphatase in nuclei. 

 Some of the cells of some organisms may, when examined by 

 the techniques given above, be lacking in phosphatase either 

 at some point in their life history, as is often the case with the 

 Protozoa, or even throughout their life history, so far as in- 

 formation is available at present. But it must be remembered 

 that none of the cytochemical methods available at present 

 for the demonstration of alkaline phosphatase are as sensitive 

 as could be desired, and that failure to demonstrate the pres- 

 ence of phosphatase in a particular site does not mean that 

 it is absent from that site, but merely that activity cannot be 

 detected by the cytochemical technique. Thus, as a general 

 rule, no alkaline phosphatase is observed by the technique of 

 Gomori in red blood cells. Nevertheless this enzyme may be 

 readily detectible in red blood cells by biochemical techniques. 



Although it is true that phosphatase has not been demon- 

 strated in the nuclei of all tissues, it is, nevertheless, true that 

 its occurrence is so common, and its distribution so striking, 

 that, had a cytochemical method for the demonstration of al- 

 kaline phosphatase preceded the discovery of the Feulgen 

 reaction, a large part of the literature on cell nuclei would almost 

 certainly have been written in terms of the distribution of this 

 enzyme. 



If, however, there is a general significance to be attached to 

 nuclear alkaline phosphatase of the same magnitude of impor- 

 tance as that to be attached to the Feulgen-positive material, it 

 should also be possible to demonstrate alkaline phosphatase in 

 the nuclei of plant cells. My first efforts to demonstrate this 

 were a complete failure. No doubt many other workers have at- 

 tempted to find alkaline phosphatase in plant-tissue nuclei by 

 cytochemical procedures but, as is the case with so many nega- 

 tive results, have not recorded the fact in the literature. How- 

 ever, after some time I discovered (accidentally) that unlike 

 the alkaline phosphatase of most animal cells, the nuclear phos- 

 phatase of plant tissues, or at least of those plant tissues which 

 I have studied, is rather rapidly destroyed by alcohol. A few 



