COAGULATED PROTEIDS 83 



albuminate may be formed by adding strong acid drop by drop to a strong 

 solution of proteid matter (e.g., undiluted egg albumin) until solidifica- 

 tion occurs. 



It is not coagulated on heating, but on exactly neutralizing the solution 

 a flocculent precipitate is produced; if it is then heated to 70 C. it will co- 

 agulate and cannot then be distinguished from any other form of coagu- 

 lated proteids. This may be shown by adding to the acid albumin solution 

 a little aqueous solution of litmus and then adding, drop by drop, a weak 

 solution of caustic potash from a buret until the red color disappears. The 

 precipitate is the derived albumin. It is soluble in dilute acid, dilute alka- 

 lies, and dilute solutions of alkaline carbonates. The solution of acid 

 albumin gives the proteid tests. The substance itself is coagulated by strong 

 acids, e.g., nitric acid, and by strong alcohol; it is insoluble in distilled water, 

 and in neutral saline solutions; it is precipitated from its solutions by satura- 

 tion with sodium chloride. On boiling in lime-water it is partially coagu- 

 lated, and a further precipitation takes place on addition to the boiled solu- 

 tion of calcium chloride, magnesium sulphate, or sodium chloride. 



Alkali Albumin. If solutions of native albumin, or coagulated albu- 

 min, or other proteid be treated with dilute or strong fixed alkali, alkali 

 albumin is produced. Solid alkali albumin (Lieberkiihn's jelly) may also 

 be prepared by adding caustic soda or potash, drop by drop, to undiluted 

 egg albumin, until the whole forms a jelly. This jelly is soluble in an excess 

 of the alkali or in dilute alkalies on boiling. A solution of alkali albumin 

 gives the tests corresponding to those of acid albumin. It is not coagulated 

 on heating except after neutralization, as in the case of acid albumin. It 

 is thrown down on neutralizing its solution, except in the presence of alkaline 

 phosphates, in which case the solution must be distinctly acid before a pre- 

 cipitate falls. 



To differentiate between acid and alkali albumin, the following method 

 may be adopted: Alkali albumin is not precipitated on exact neutralization 

 if sodium phosphate has been previously added. Acid albumin is precipi- 

 tated on exact neutralization, whether or not sodium phosphate has been 

 previously added. 



Coagulated Proteids. These are formed by the action of heat 

 or of ferments upon other proteids; the temperature necessary to produce 

 coagulation varying in the manner previously indicated. They may also 

 be produced by the prolonged action of alcohol upon proteids; the process 

 is one of dehydration. They are soluble in strong acids or alkalies; slightly 

 so in dilute; are soluble in digestive fluids (gastric and pancreatic), and are 

 insoluble in water or saline solutions (except fibrin). 



Fibrin is formed by the action of fibrin ferment on fibrinogen and can be 

 obtained as a soft, white, fibrous, and very elastic substance by whipping 

 blood with a bundle of twigs and washing the adhering mass in a stream of 



