ALKALINE PHOSPHATES OF CELL NUCLEI 51 



the superimposed-section technique described earlier in this 

 chapter (p. 37). Plate IV shows some of the results obtained 

 when kidney sections containing active enzyme were superim- 

 posed upon kidney sections in which the enzyme had been in- 

 activated. The sections were incubated for periods as follows: 

 5, 10, 20, 40, 80, 160, 320, 640, and 1280 minutes. Plate IV, 

 Fig. B, shows that the nuclei of the proximal tubules in the sec- 

 tion containing active enzymes are positive for phosphatase in 

 the case of the rat kidney after only 5 minutes' incubation. 

 Guinea-pig kidney in our experience has usually required 10 

 minutes' incubation to demonstrate the intrinsic phosphatase. 

 At this time no phosphatase has appeared in the inactivated 

 underlying section. Plate IV, Fig. C, shows the result obtained 

 after 320 minutes' incubation with the rat kidney. The section 

 containing active enzymes has produced so vigorous a reaction 

 for phosphatase that it is no longer possible to see all the detail 

 of distribution of the enzyme. The underlying section is still 

 devoid of phosphatase activity. Plate IV, Fig. D, shows the re- 

 sult obtained in the underlying inert section after 640 minutes' 

 incubation. The amount of phosphatase which is demonstrated 

 in the inert section is comparable with that found in the section 

 containing active enzyme after only 4 or 5 minutes' incubation. 

 When kidneys from different animals are studied in this way, 

 there is some variation in the time at which evidence of dif- 

 fusion of phosphatase is manifest. Sometimes in the guinea- 

 pig kidney phosphatase may appear in the underlying section 

 after only 320 minutes' incubation. The amount of phosphatase 

 which may have diffused into the underlying section after a 

 lengthy period of incubation (1280 minutes) is considerable. 

 With the material which we have investigated, we have never 

 found any considerable amount of diffusible phosphatase in rat 

 kidney revealed with incubations of 320 minutes or less. But 

 sometimes, after 1280 minutes' incubation with guinea-pig kid- 

 ney, there may be a very heavy reaction in the underlying sec- 

 tion. This reaction, of course, is entirely due to diffusion arte- 

 facts. 



It is clear from these results that the phosphatase which is 

 seen in the nuclei of kidney after periods of incubation up to 

 160 minutes is intrinsic phosphatase. After twice this period 

 it is possible that part of the reaction observed is due to diffu- 



