That a formative act such as is here referred to is actually going on within the human urinary apparatus, is also rendered probable from the examination of stones immediately after they have been re moved entire, as by lithotomy. It will be found they are covered with a distinct layer of viscid mucus, which often adheres with such tenacity as to require washing, with friction, before it can be entirely removed. The conditions under which this process of stone formation by molecular coalescence proceeds seem not yet determined. That there is some affinitive attraction between the various kinds of inorganic particles engaged which may be regulated by those in excess, through the medium of the colloid, is not improbable, other wise it would be difficult to understand how grouping takes place with such precision.
The view thus entertained as to the formation of calculi by molecular coalescence through the intervention of colloid has had weight incidentally given to •it by some remarks of Mr. Cadge in his address before the British Medical Association, at the annual meet ing at Norwich in 1874. Referring to matters connected with diet, he observes that "the prevalence of stone amongst the children of the poor is largely due to their not obtaining a proper and suffi cient supply of sound milk," and that the abundance of stone in children " will be found in strict accordance with the difficulty of procuring milk." That is to say, in place of a fluid food which is generally regarded as unirritating to the urinary organs, others are substituted of an opposite nature, and thus the urinary mucus is con siderably increased. I have had frequent opportunity for verifying this observation. Dr. Plowright " more directly supports the colloid view, but from a somewhat different standpoint. In reference to the use of salt as an article of diet, he observes : " (a) That the presence of salt greatly increases the solubility of uric acid; (b) that the con sumption of salt by increasing thirst insures a larger amount of fluid passing through the urinary tract, and therefore lessens the proba bility of calculus; (c) that by keeping the colloids equally diffused, salt tends to prevent the crystalline solids of the urine from agglom erating into calculi." Dr. Plowright found from experiment that the addition of 2 per cent of salt quadrupled the solubility of uric acid.
It has long been noticed, as Prout remarked, that " hard waters have a great influence in producing stone." Mr. Cadge also observes that " the balance of evidence was in favor of stone cases being con nected with hard drinking-water." In various neighborhoods, I am
told, the change from a hard to a soft drinking-water by the substitu tion of an artificial supply has resulted in a considerable diminution of stone cases. From some observations I have noticed that corre sponding variations in the quality and quantity of urinary mucus follow the drinking of waters of different degrees of hardness.
It would therefore appear probable that the intercurrence of pro vision for the supply of a suitable colloid in the urinary passages may be sufficient in itself to favor the formation of gravel and stone without any necessary alteration in the amount of the urinary solids.
For, assuming that eight or ten grains of so insoluble a deposit as lithic acid is daily excreted," it seems to me that there is not an in dividual in fair health who is incapable of forming a stone in a reasonable time, provided that the circumstances for concretion are favorable. If, for instance, a man in the habit of excreting ten grains of lithe acid a day was only to void half this with his urine, and concrete the remainder, it is obvious he might form a stone of this material alone, weighing not less than half an ounce, in something like forty-eight days. In a woman the probabilities of her forming a stone are very considerably less, not because she necessarily excretes less lithic acid, but by her different mechanism for urination, not to say anything of the absence of a muscular ring or buttress at the neck of the bladder like the prostate. In her case the earlier nuclei of stone are tolerably sure to make their escape from the bladder, as it is only when a calculus too large to pass through the from the kidney, that the possibility of an increase, in this position, is at all likely to occur. The rate at which triple phosphates will concrete in both sexes, owing mainly to the rapidity with which they are capable of being produced, is sometimes very remarkable. Though Ethic acid may be the predominating calculus of the Eastern coun ties in England, I do not see it asserted that the urine of the inhabi tants contains it in excess as compared with those residing in other districts. In the expression, " it may be that the abundance of stone in Norfolk is due not to actual excess, but to circumstances which merely determine the precipitation and separation of lithic acid in the urinary tract," Mr. Cadge" almost offers the explanation I am venturing to lay some stress upon.