CARBONATE OF LIME. 421 



the inner car, on whose outer and upper walls it is deposited in 

 minute crystals amongst organic matter. These crystals are usually 

 so very minute,, that distinct molecular motion may be observed 

 amongst the smallest of them. The form of the crystals is never 

 a pure rhombohedron, but always a prism derivable from the 

 rhombohedron of calc-spar, most frequently resembling the so- 

 called Kanonendrusen of calc-spar ;* that is to say, they are six-sided 

 with 3-planed acuminations. Kriegerf has also seen twin crystals 

 of the scaleno-octahedral form. Crystals of this nature occur 

 much more frequently and abundantly in the lower animals, both 

 in the organs of hearing and in other parts; perhaps the best 

 known and most striking case of the occurrence of such crystals is 

 in the membrane of the brain of the batrachia, and in the white, 

 silvery saccules at the intervertebral foramina through which the 

 spinal nerves emerge. In morbid formations in the human organ- 

 ism, we not unfrequently meet with crystalline deposits of carbonate 

 of lime, which however usually appears rather in irregular crystal- 

 line masses, such as are described by Vogel,J than as perfectly 

 formed crystals. 



There are obviously two ways in which we may account for 

 the presence of carbonate of lime in the animal organism. It is 

 well known that spring water holding carbonic acid in solution, 

 usually contains a considerable quantity of carbonate of lime ; and 

 this might sufficiently explain the presence of this salt, even if it 

 were not in a great measure formed within the organism from 

 other salts of lime, which find their way there in abundant quan- 

 tity with the vegetable articles of food ; hence it is that the urine 

 of herbivorous animals is often so rich in carbonate of lime. 



The solubility of this salt in the animal fluids, might, at first 

 sight, seem to be less easily understood than its origin. The free 

 carbonic acid which, it is almost certain, may be detected in all 

 the animal fluids, doubtless acts as a solvent for the carbonate of 

 lime ; and I may remind any who may not be satisfied with this 

 explanation, that the old experiments of Guiton Morveau, show 

 that carbonate of lime is also slightly soluble in solutions of the 

 alkaline salts, as for instance, chloride of potassium. Moreover, 



* [The term Kanonendrusen is used in the Hartz to signify a crystalline mo- 

 dification of calc-spar. Drusen signifies a cluster of crystalline substances. A 

 crystal is said to be drusy (drusig) when it is coated with a number of minute 

 crystals of the same kind, so that the new surface acquires a scaly aspect. G. E. D.] 



t De otolithis. Berolini, 1840, p. J5. 



J Icones histol. path. Tab. 22, fig. 8. 



