tain whether these could be deteoted in their passage through the
blood, from the stomach to the bladder.
The method employed by the author for detecting sugar in the serum, was first to add dilute muriatic acid to the serum, and then to heat it till perfectly coagulated. The water which exudes from healthy serum so coagulated, contains scarcely anything but salts, which crystallize by evaporation. But if a very small proportion of sugar has been previously added, it is immediately detected upon _ evaporating a drop of this fluid, by the blackness and interruption to the crystallization which are occasioned by it. As a further test of the presence or absence of sugar, a little nitric acid was added to the drop, which in the former case merely occasioned an alteration in the form of the salts, but in the latter a white foam rises round the mar- gin of the drop, and it subsequently turns black.
The author next examined the blood of four persons labouring under diabetes. whose urine contained sugar, and was satisfied that no one of them contained a perceptible _quantity of sugar.
Since the formation of sugar did not appear so likely to arise from a new power assumed by the kidneys in diabetes, as from a process of imperfect assimilation by the stomach, and since the possibility of fluids passing from the stomach to the bladder without passing through the blood, had been formerly maintained by Dr. Darwin, it seemed desirable to examine this point by some test more decisive than nitre, which was employed byDr. Darwin. Dr. Wollaston, therefore, made use of prussiate of potash for this purpose, which he found might be taken without detriment or inconvenience, and could be detected with the utmost facility in the urine by adding solutions of iron. Nevertheless, no perceptible quantity of this prussiate could be dis- covered in the blood taken from the arm during the secretion of urine highly impregnated with it. ,
The author also examined other secretions, as the saliva. and the fluid secreted by the nose during a catarrh; but he could not perceive them to be tinged with the prussiate.
He is consequently much inclined to the opinion, of the existence of some channel of conveyance from the stomach to the bladder, not yet rightly understood. For though the agency of an elective power, residing in the nerves as acting cause, may account for the transfer, yet the channel through which they are conveyed remains to be discovered by direct experiments on living animals, which he has not been inclined to undertake.
