12 PRACTICAL PHYSIOLOGY. [l. 



water is heated by passing through a coil of tubing contained in a copper 

 vessel, not unlike Fletcher's hot-water apparatus. The Huid to be tested 

 must be well stirred by the thermometer during the progress of the experi- 

 ment. 



In carrying out the experiment the following precautions are necessary, 

 viz., to keep the fluid under investigation as nearly as possible always of the 

 same reaction, as one of the important conditions inHuencing the temperature 

 of coagulation of a liquid is the amount of free acid present. 



Use 2 per cent, acetic acid, and place it in a burette. It is dropped into 

 the fluid from tlie burette. The proportion is about one drop ot this dilute acid 

 — after neutrality is reached— to 3 cc. of liquid. The acidity of the liquid is 

 tested by sensitive litmus papers. The liquid must be kept at a given 

 temperature for at least five minutes, to ensure complete precipitation of the 

 proteid at that temperature. 



On heating certain solutions containing certain proteids, as the tempera 

 ture of the fluid is raised, a faint opalescence appears first, and then, at a 

 higher temperature, masses or flocculi separate out, usually somewhat 

 suddenly, from the fluid. 



The temperature at which coagulation of what is apparently one and the 

 same proteid occurs varies wth a large number of conditions. Not only have 

 diflerent proteids diff'erent coagulating points, which, however, can hardly in 

 the light of recent researches be called "specific coagulation temperatures," 

 but the coagulating temperature of any one proteid varies with the rapidity 

 with which coagulation takes place ; the proteid coagulates at a higher 

 temperature when the fluid is heated quickly than if it be heated slowly. 

 It also varies with the amount of dilution, the coagulating point being raised 

 by dilution. The eHects of salts and acids in altering the coagulation point 

 are well known. 



14. Removal of Proteids. — The following, amongst other methods, 

 are used for removing proteids from liquids containing them. In 

 tliis way other substances present may be more easily detected. 



Wenz^s Method. — Saturate with (NHj)^ SO4. This precipitates all proteids 

 except peptones. 



By Boiling. — Acidulate faintly with acetic acid and boil. This removes 

 globulins and albumins. 



Brackets Mel hod. — Acidulate with HOI, and then add potassio-mercuric 

 iodide (see " Liver "). 



By Alcohol. — Acidify feebly with acetic acid, add several volumes of 

 absolute alcohol. After 24 hours all proteid is precipitated. 



Oirgensohu's Metho'l. — Mix the solution with half its volume of a saturated 

 solution of sodium chloride, and add tannic acid in slight excess. This pre- 

 cipitates all proteids. 



There are other methods in use. 



