PROTEWS. 413 



occurs in urine. Obtained from blood-serum by saturating it at 

 30 C. (86 F.) with magnesium sulphate, which precipitates globulin ; 

 the filtered solution is saturated at 40 C. (104 F.) with sodium 

 sulphate, when the serum-albumin is precipitated. Thus obtained, 

 it is not quite pure, but contains some salts which may be eliminated 

 by dissolving the precipitate in water and subjecting the solution to 

 dialysis. 



Pure serum-albumin is an almost white, or pale-yellow, elastic 

 substance, dissolving readily in water to a slightly alkaline, opales- 

 cent solution, which coagulates by heating to 50 C. (122 F.), while 

 the addition of sodium chloride raises the coagulating-point to 75- 

 80 C. (167-176 F,). It is not readily coagulated by alcohol or 

 precipitated by ether. It turns the plane of polarized light to the left. 



b. Egg-albumin differs but little from the former, but may be dis- 

 tinguished from it by being coagulated by ether, which does not affect 

 serum-albumin. It exists in solution in the white of eggs, where it 

 is contained in a network of delicate membranes. 



G. Vegetable albumin exists in nearly all vegetable juices, and is a 

 valuable constituent of vegetables used as food. It is coagulated at 

 61-63 C. (142-146 F.), and by nearly all acids. 



Class II. Globulins. They are, like native albumins, coagulated 

 by heat, but differ from them by not being soluble in pure water ; 

 they are soluble in dilute solutions of neutral salts of the alkalies or 

 alkaline earths (such as sodium or potassium chloride, sodium or 

 magnesium sulphate, etc.), but are in most cases precipitated by 

 saturated solutions of the salts mentioned, as also by passing a cur- 

 rent of carbon dioxide through their solutions. 



a. Paraglobulin or Serum- globulin. This substance is found in 

 considerable quantity in blood-serum, constituting about one-half of 

 its total proteids ; it also occurs in lymph. The most satisfactory 

 method of preparing paraglobulin is to saturate blood-serum with 

 magnesium sulphate at a temperature of 30 C. (86 F.), when it is 

 precipitated and purified by washing it upon a filter, first with a solu- 

 tion of magnesium sulphate, and then with water. Paraglobulin 

 shows the general properties mentioned above as characteristic of 

 globulins. 



b. Fibrinogen is the name given to a substance found in blood- 

 plasma, chyle, lymph, and other coagulable fluids of the body. On 

 contact with a peculiar ferment (fibrin-ferment), it is converted into 

 fibrin, thereby giving rise to the phenomenon of coagulation. 



