99 
of Sugar in the Blood , 
porated, the salts which it contains are found to crystallize, so 
that the form of the crystals may be easily distinguished ; they 
are principally common salt. 
If any portion of saccharine matter has been added to the 
serum previous to coagulation, the crystallization of the salts 
is impeded, or wholly prevented, according to the quantity of 
sugar present. 
If the quantity added does not exceed two grains and a half 
to the ounce, the crystallization is not prevented ; but even 
this small quantity is perceptible by a degree of blackness that 
appears after evaporation : occasioned, as I suppose, by the 
action of a small excess of acid on the sugar. 
If five grains have been added, the crystallization is very 
imperfect, and soon disappears in a moist air by deliquescence 
of the sugar. The blackness is also deeper than in the former 
case. 
By addition of ten grains to the ounce, the crystallization of 
the salts is entirely prevented, and the degree of blackness, 
and disposition to deliquesce are of course more manifest than 
with smaller quantities.* 
As I was aware that the sugar obtained from diabetic urine 
is a different substance from common sugar (approaching 
more nearly to the sugar of figs), I had the precaution to re- 
peat the same series of experiments upon serum, to which I 
made corresponding additions of dry sugar, that I had for- 
merly extracted from the urine of a person who voided it in 
considerable quantity ; and I found the effects to be perfectly 
similar in every respect. 
* In the annexed Plate are represented the degrees of blackness of the drop occa- 
sioned by adding one, two, three, and four grains of sugar to six drachms of serum. 
O 2 
