362 Proceedings of Royal Society of Edinburgh. [sess. 
occur; thus, keeping to the example, egg albumen, Wurtz 
puts the coagulation point at 73° C., and Henrijean at 60° to 
61° C. 
It is hardly possible to explain such differences, either on the 
assumption that any of the above authors had used imperfect 
apparatus, or, that they had been guilty of inaccurate observa- 
tion. It is more probable that the conditions, under which the 
experiments were performed, were not always the same. What 
are the conditions which are capable of modifying the coagulation 
point of albumen % It seemed to us a not unimportant point to 
investigate systematically these conditions ; as such investigation 
is calculated to throw light on the nature of coagulation itself, and 
may enable one to arrive at the exact specific coagulation points of 
the more important proteids, heated as they should always he 
under exactly similar conditions. The conditions modifying 
coagulation, which we have studied, are, — the rapidity at which 
the coagulation is allowed to take place, the degree of concentration 
of the proteid substance itself, the presence of acids and alkalies, 
and the presence of soluble salts. 
The Rapidity at which Coagulation is allowed to take place. 
This is an acknowledged factor varying the indicated temperature 
of coagulation, and at least one author has alluded to it in the case 
of the particular albumen studied by himself. If a solution of a 
coagulable proteid be heated quickly, the proteid will be found to 
coagulate at a higher temperature than if the heat be applied more 
slowly. Thus we found that egg albumen, diluted with one volume 
of water, coagulated at 64° C., when slowly heated, the temperature 
taking forty minutes to reach this point. Another portion of the 
same solution coagulated at 66° C., when heated rapidly, the 
experiment taking in this case only one minute. It is not difficult 
to explain this fact. If a drop of an albuminous fluid is mounted 
for microscopical examination, and, if it he heated on the stage of 
the microscope, the process of coagulation can he readily followed 
out. When opalescent, the fluid will be found to contain numbers 
of tiny granules. These granules increase in size, and apparently 
become adherent, and run together to form granular masses or 
flocculi. This naturally requires time, and if the fluid be heated 
