1884.] The Proteids of Serum. 103 



bath ; the substance under investigation being placed in a test-tube 

 contained within the inner beaker.* The chief objection to that 

 method is that the rise of temperature in the water in the beakers 

 takes place with extreme slowness, so that changes are apt to occur in 

 the proteid during the experiment. To meet this difficulty an 

 apparatus was devised by Professor Schafer, which was found to be 

 extremely easy to use, and of which the great advantage consists in 

 the readiness with which a constant temperature is maintained for a 

 considerable time. It may be briefly described thus : the liquid of 

 which one wishes to determine the temperature of coagulation is 

 placed in a test-tube in sufficient quantity to cover the bulb of a 

 thermometer put into it; the test-tube is placed in the neck of a 

 flask containing water ; this water is kept at the desired temperature 

 by the following means. It is in the first place kept constantly 

 running, entering by one tube and leaving the flask by another tube 

 inserted as a T-piece in the upper part of the neck. The water is 

 warmed by passing it through a coil of tubing contained in a vessel 

 in which water is kept constantly boiling. By regulating the rate at 

 which the water flows through this apparatus the desired temperature 

 is maintained. 



The temperature of coagulation of serum-globulin is stated to be 

 75 C., and that of serum-albumin as 73 C. But it was found that 

 after heating serum to the higher of these two temperatures, and 

 filtering off the coagulum, that the filtrate still contained a large 

 amount of proteid, which coagulated at a temperature higher than 

 75 C. 



A method of fractional heat-coagulation was therefore adopted. 

 A specimen of serum was taken, and heated until a flocculent preci- 

 pitate appeared ; this was filtered off, and the filtrate again heated 

 until another deposit took place ; this was repeated until the filtrate 

 gave no evidence of the presence of proteid. In order to obtain these 

 precipitates it was necessary to render the liquid faintly acid ; if this 

 is not done alkali-albumin is formed, which will not coagulate. It is 

 also necessary to render faintly acid each filtrate, as after the separa- 

 tion from it of a precipitate, a faintly acid liquid becomes neutral, or 

 faintly alkaline. Acetic acid was the acid used for this purpose in 

 most instances. 



By this means it was found that the albumin of serum can be 

 differentiated into three different proteids, which coagulate at the 

 temperatures of 73 C., 77 C., and 84 C. These temperatures vary 

 within certain limits, the presence of excess of certain salts to be 

 afterwards noted raising or lowering the temperature somewhat ; and 

 it is found that the amount of acid present has a very marked effect 



* Gamgee's " Physiological Chemistry," p. 15. 



