380 Proceedings of Royal Society of Edinburgh. [sess. 
are at once coagulated after the addition of a few drops of weak 
acid. No one has brought this out more clearly than Dr Halli- 
burton in a most suggestive paper (Reference 6), which will pre- 
sently be quoted in relationship to fractional coagulation. He 
showed that the coagulation point of serum albumen varies with 
the amount of acid present, the greater the quantity added, the 
lower the coagulation point, until finally coagulation could be 
produced at the temperature of the laboratory. If then the co- 
agulating point depended on the two factors, heat and the amount 
of acidity, it seemed to him a natural deduction, that, on keeping 
one of these, the acidity, a constant quantity, it might be possible 
to separate by fractional coagulation two or more albumens mixed 
together, and having different coagulation points. He investi- 
gated serum albumen, and found that if it be neutralised by the 
addition of some drops of a 2 per cent, solution of acetic acid, 
and if, further, it be rendered slightly acid by the addition of one 
drop of the dilute acetic acid to seventy-five drops of the albuminous 
solution, then it coagulates at 70° to 71° C., and if this coagulum be 
filtered off, and the solution again brought to the same degree of 
acidity, a coagulum occurs the second time at 77° to 78° C. If this 
coagulum be filtered off and the filtrate acidified as before, a third 
coagulum may be produced at 82° C. Dr Halliburton considers 
that the serum albumen, originally regarded as one proteid, in 
reality consists of three. 
MM. Corin and Berard have followed this process of fractional 
coagulation, applying it to egg-white. This substance, commonly 
held to consist of albumen and globulin, they believe to consist of 
three albumens and two globulins. 
They neutralise some egg-white, slightly acidify it, and raise its 
temperature, until opalescence appears; then they keep the tem- 
perature constant for a considerable time — an hour or even more. 
They filter off the coagula, re-acidify to the same degree, raise the 
temperature until opalescence occurs, and then after more prolonged 
heating flocculi again appear. 
In this way they have succeeded, as already stated, in fractionating 
five proteids. 
Without doubting that it may be possible to fractionate some 
proteids, nevertheless the results of our own work, and many of 
