Infrastructural and Crystallographic Study of Experimental Calcifications 167 



Granular rosette-like deposits are observed in mitochondria in an early stage. On the 

 other hand, injections of calcium gluconate produce granular deposits arranged in 

 concentric lamellae, located in the basement membrane of the proximal convoluted 

 tubule. They do not diffract the electrons and are ascribed to calcium carbonate and 

 related to the activity of the carbonic anhydrase. 



Renal deposits of apatite were observed by Gershoff and Andrus (1961) in 

 rats fed with a diet rich in calcium and poor in magnesium. 



Human extracellular deposits diffracting electrons but giving no interpretable 

 pattern were also observed by Galle (1962). Devik's experiments (1962) provide 

 precise information on the periodic precipitation of calcium phosphates to explain 

 the mechanism of formation of Liesegang rings in extracellular deposits. 



According to Howell et al. (1961), the presence of cells, connective tissue fibers 

 and fundamental substance is necessary to induce the deposit of mineral matter 

 around sponges. An enzymatic reaction or other local factors are possibly induced 

 by such elements. Polyvinyl sponges produce a strong reaction which is weakened by 

 a preliminary treatment of the sponges with silicones; sponges of cellulose acetate 

 give a moderate reaction while polyurethane sponges give a negative one. 



Acknowledgement 

 Acknowledgement is made of the assistance given by Miss S. Pregermain, Mrs. 

 Normand-Reuet, Mr. C. Alexanian for electron diffraction and by Mr. P. Henoc 

 (C.N.E.T. Issy-les-Moulineaux) and Miss S. Durif for X-ray diffraction. 



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