392 



tain whether these could be detected 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 by Dr. 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 per- 

 ceive 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 dis- 

 covered by direct experiments on living animals, which he has not 

 been inclined to undertake. 



