. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PRODUCTS, ADVENTITIOUS. 77 single substance, are termed simple ; of several, compound. When the different materials are applied in successive laminae, the calculus is said to be alternating (/g. 76) ; when they are irregularly mingled it is called mixed. The relative frequency of the three kinds may be deduced as follows from tables printed by Dr. Front. Of 1520 calculi there were SIMPLE, 709 ; Alternating, 787 ; Mixed 24. The mode of succession of various substances in the formation of alternating calculi (they may cons
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PRODUCTS, ADVENTITIOUS. 77 single substance, are termed simple ; of several, compound. When the different materials are applied in successive laminae, the calculus is said to be alternating (/g. 76) ; when they are irregularly mingled it is called mixed. The relative frequency of the three kinds may be deduced as follows from tables printed by Dr. Front. Of 1520 calculi there were SIMPLE, 709 ; Alternating, 787 ; Mixed 24. The mode of succession of various substances in the formation of alternating calculi (they may consist of two, three, four, or several suc- cessive strata), is pathologically important, and has been specially investigated by Dr. Prout. The nature of this work prevents us from en- tering into the subject, but we may mention (as evidence of the generality of Dr. Front's law, that the existence of mixed phosphates in a calculus excludes the subsequent deposition of other matter), that of 566 alternating calculi composed of two layers, two only were examples of a nucleus of phosphates with a cortex of another kind of salt; that of 172 calculi formed of three layers, not one had a phosphatic nu- cleus, and in only three was the middle atratum composed of phosphates ; and that, lastly, of 25 calculi containing four distinct layers, not one had a nucleus of phosphates ; in one only was the second layer, and in three only was the third layer, thus composed. It is, however, right to observe that if small quantities of phosphates, not forming actual layers, were taken into consideration, the exceptions to the law would be much more numerous. The degree of rapidity with which calculi form and acquire bulk depends upon the con- stitutional condition of the individual in whom they form, much more than upon the nature of their own ingredients ; for, if it be true that oxalate of lime and uric acid calculi commonly enlarge slowly, and the phosphatic species with great quickness, instances
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