102 Dr. Wollaston on the Non-existence 
I unfortunately had no opportunity of repeating the experi- 
ment on a second portion of the same serum, having inconsi- 
derately employed it for other experiments, and coagulated it 
at the same time with the former. 
In the next experiment I added half a dram of the urine 
of the same person to six drams of the serum and with a due 
proportion of diluted muriatic acid coagulated as before. Al- 
though the quantity of extract added did not exceed -ff , or two 
grains and a quarter of extract, the difference was very mani- 
fest by the darkness of the colour and the defective crystalli- 
zation of the salts. 
To the remaining quantity of the serum I had added twice 
the former proportion of the urine, and found that this quan- 
tity did not wholly prevent the crystallization of the salts 
during the evaporation of the drop. 
The result of these trials was such, as to satisfy me that the 
serum in this instance contained no perceptible quantity of 
sugar, or at least that the water separable from the coagulated 
serum did not contain one-thirtieth part of that proportion 
which I had found in the urine of the same person. 
In order to account for the presence of sugar in the urine, 
we must consequently either suppose a power in the kidneys 
of forming this new product by secretion, which does not 
seem to accord with the proper office of that organ ; or, if we 
suppose the sugar to be formed in the stomach by a process 
of imperfect assimilation, we must then admit the existence of 
some channel of conveyance from the stomach to the bladder, 
without passing through the general system of blood-vessels. 
That some such channel does exist, Dr. Darwin* endeavoured 
* Account of the retrograde Motion of the absorbent Vessels, by Charles 
Darw i N. 
