382 Proceedings of Royal Society of Edinburgh. [sess. 
tion into two portions, A and B, and heat A to 75° C., and keep B 
at the original temperature. A will coagulate, showing that although 
in too dilute a solution to coagulate below 70° C., it could neverthe- 
less coagulate, provided its temperature he raised. B will remain 
clear, hut, if more albumen be dropped into it, a point will be 
reached, at which it will cease to dissolve, and then it will separate 
out in flocculi. 
Here then, without going any further, one has come across an 
observation which, if it does not explain all the facts described under 
the head of fractional coagulation, must at any rate account for 
some of them. 
Both Dr Halliburton and MM. Corin and Berard found that 
after coagulation the filtrate, which they separated from the clot, 
was less acid than it was before coagulation had occurred, the latter 
observers finding that, as a rule, it was actually alkaline. Here, 
again, is a factor which we cannot afford to lose sight of. If the 
coagulation point is lowered by acidity, as all persons are agreed, one 
would expect that, while coagulation is proceeding, and while pari 
passu the acidity is decreasing, that the decrease of acidity would at 
last bring the coagulation — at that temperature — to a standstill. 
In this case one would expect, that on re-acidifying to the same 
degree, another crop of coagula might fall at the same temperature 
as did the first crop. 
Dr Halliburton does not mention any such coagulation, although 
undoubtedly it occurs, and we have found it on repeating his ob- 
servations, but MM. Corin and Berard evidently find that one is 
produced, and in consequence they heat the albumen for an hour or 
more before filtering off the coagulum. After this time, they found 
that the albumen never gave a second coagulation at the same 
temperature. We cannot but conclude from this that their experi- 
ments clearly indicate that the albuminous solutions with which 
they worked must have been very materially changed by the 
temperature, nor is it at all improbable that very material changes 
may occur in a solution of egg albumen kept in an acid solution at 
a high temperature for over an hour ; in one of their quoted experi- 
ments fractionation lasted over six hours. 
We may, we think, make this statement, and one fully borne out 
by our own experiments, that during coagulation in an acid medium 
