Hvnxc'xrr. fixation in osmium tftroxidr after completion of the histo- 

 ohemiortl incubations is roquired to relate the site of the final product 

 of tho roaotion to fine structure as the latter is now accepted. The 

 results of several cxperiments combininj^ thèse techniques and concerned 

 with the relationship of ovidative or hvdrolytic enzvme activitv with fine 

 structure xvill be prescnted. 



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