OCCURRENCE OF PATHOLOGICAL CALCIFICATION 367 



caseous areas, and particularly in old inspissated collections of 

 pus. It may be said that any area of dead tissue that is not 

 infected, and that is so large or so situated that it cannot be 

 absorbed, will probably become infiltrated with lime salts. 

 Most frequently calcified, next to totally necrotic tissues, are 

 masses of scar-tissue that have become hyaline subsequent to 

 the shutting off of circulation in the scar by contraction of the 

 tissue about the vessels. Elastic tissue also seems prone to an 

 early calcification, and it is not uncommon to see the elastic 

 laminae of small arteries calcified in an apparently selective 

 manner. A peculiar form of calcification is that frequently 

 found in ganglion-cells of the brain which have become degen- 

 erated or necrotic, particularly in the vicinity of old hemor- 

 rhages ; the cells become infiltrated with lime salts until a 

 complete cast of the cell, with dendrites and axis-cylinder well 

 impregnated, is formed. The calcification of renal epithelium 

 obtained experimentally by ligation of the renal vessels or by 

 the administration of certain poisons, is considered by some to 

 be more closely related to the formation of ordinary urinary 

 concretions than to tissue calcification ; in any event, because of 

 the function of the renal tissues to excrete calcium, and the 

 continuous bathing of the cells with calcium-containing urine, 

 the conditions are quite different from what they are in ossifi- 

 cation and other forms of pathological calcification. Calcifi- 

 cation of epithelial cells does occur, however, and seems to 

 be preceded by hyaline changes, in which hyaline substance 

 the calcium is later deposited, as in epithelial pearls, for 

 example. 



LeNoir l attempts to lay down a law of calcification, as follows : 

 " We know that certain pigments are fixed first in the tissues possessing 

 the most feeble vitality. Charrin and Carnot have shown that mineral 

 poisons (lead) accumulate by choice in tissue previously altered. The 

 organism, therefore, seems to have a tendency to rid itself of valueless 

 or toxic compounds in tissues where nutrition is least active. Lime 

 salts do not form an exception to the general rule ; if they are in excess 

 in the blood, they accumulate in the cells that are necrobiotic, or in 

 cells in which the vitality is feeble, and there are deposited in an in- 

 soluble condition." This law is expressed in rather too metaphysical a 

 manner, but it probably contains a kernel of fact, 



Metastatic Calcification. What is perhaps the only ex- 

 ception to the rule that some form of tissue degeneration is 

 required before calcification occurs is the " metastatic calcification" 



1 Bouchard's Path. Gn6rale, vol. 3, pt. 2, p. 650. 



