TO CALCULOUS DISEASES. 
419 
soda and potash. They gradually dissolved, evolving carbonic acid ; and a 
solution of the mass, when cold, being made in water, and neutralized by mu- 
riatic acid, gelatinized silica was thrown down from it. A slight excess of 
muriatic acid was then added, and the whole evaporated to dryness. After 
withdrawing the muriate of potash and soda by distilled water, the silica was 
left in its usual white, insoluble state. By comparing the magnitude of these 
granules with some which were taken from a sand bath, it was calculated that 
they did not average more than the 400th part of a grain in weight. The 
granules were thus unequivocally proved to be of silex ; and as they were im- 
bedded in, and diffused through, oxalate of lime, a substance of known urinary 
origin, it is impossible to avoid the conclusion, that the production, or deposi- 
tion of these two substances, went on simultaneously. 
I am the more particular in mentioning the circumstances under which the 
siliceous deposit exhibited itself, because much discrimination is occasionally 
necessary, on the part of medical men, to prevent their being deceived, by the 
mistakes of patients, or their friends, in matters of an unusual nature. And as 
if the love of exciting surprise and admiration by the marvellous, were not 
confined to the traveller, there is sometimes found in patients, however sin- 
gular the fact may appear, an inclination to impose on their professional 
attendants, by the description or exhibition of something strange and ano- 
malous*. 
There are only three instances on record, as far as I know, of the existence 
of silex in urinary calculi. Two are mentioned by MM. Fourcroy and 
Vauquelin as occurring among 600 calculi which they analysed ; and here 
the silex was found blended with oxalate of lime, as in the specimen which I 
have mentioned. The third was observed by Prof. Wurzer, and its principal 
ingredients were phosphate of lime and lithic acid, the weight of the calculus 
being 870 grains, and the quantity of silex being one per cent.-f'-. In none of 
these calculi, however, is the magnitude of the siliceous particles stated. 
The deposition of siliceous gravel is mentioned by Dr. Venables of Chelms- 
ford, in a communication published in the Quarterly Journal of Science, Lite- 
* Portions of coal, brick, common gravel, and sea shingle, have occasionally been produced, as of 
urinary origin. 
t Annales de Chimie, tome lx. p. 313. 
