328 HAND-BOOK OF PHYSIOLOGY. 



in being soluble in ether and in not so easily giving a precipitate with 

 strong hydrochloric acid; the precipitate being easily redissolved in excess 

 of the acid. Serum-albumin is found in the blood, lymph and serous and 

 synovial fluids, and the tissues generally; it appears in the urine in the 

 condition known as albuminuria. Two varieties, metalbumin and paral- 

 lumin have been described as existing in dropsical fluids and ovarian 

 cysts respectively. 



II. Derived Albumins are made by adding dilute acids or alkalies 

 to solutions of native-albumin. They are insoluble in water or in neutral 

 saline solutions, and are not coagulated by heat. Both the native-albu- 

 mins and the next two classes (iii. and iv.) of proteids generally undergo 

 change into either acid or alkali albumin on the addition of acids or al- 

 kalies, and foods containing either albumins or globulins change first of 

 all into one or other of these compounds, according as they are acted 

 upon by the gastric or pancreatic juices respectively. Acid- albumin is 

 called also syntonin, and is either identical with or akin to it. Casein is 

 very probably natural alkali-albumin, and exists in milk, being kept in 

 solution by the alkaline phosphates; it exists also in the serum and serous 

 fluids in small quantity, and in muscle. It is not coagulable by heat, and 

 so corresponds with the other derived albumins; it is obtainable as a pre- 

 cipitate by neutralizing milk with acid (acetic). Naturally it is precipi- 

 tated in sour milk, on the formation of lactic acid. 



III. Globulins which comprise the fibrin-forming substances of the 

 blood and the coagulable material in muscle, and also the principal part 

 of the crystalline lens, yelk of egg, etc., are soluble in very dilute saline 

 solutions, but not in distilled water like the native-albumins; on addition 

 of an acid or alkali, they are converted into the corresponding derived- 

 albumin. They are precipitated on heating. The following are the 

 chief varieties of globulins. 



(a.) Globulin or Crystallin is prepared by rubbing up the crystalline 

 lens with sand, adding water and filtering. On passing a current of car- 

 bonic acid gas through the filtrate, globulin is precipitated. In proper- 

 ties, it resembles fibrino-plastin and fibrinogen, but cannot apparently 

 produce fibrin in fluids containing either. It coagulates at 70 75 C. 



(b.) Myosin can be prepared (1) from dead muscle by removing all 

 fat, tendon, etc., and washing repeatedly in water, until the washing 

 contains no trace of proteids, and then treating with 10 per cent, solution 

 of sodium chloride, which will dissolve a large proportion into a viscid 

 fluid, which filters with difficulty. If the viscid filtrate be dropped little 

 by little into a large quantity of distilled water, a white flocculent pre- 

 cipitate of myosin will occur. (2) Or from living muscle by freezing and 

 rubbing up in a mortar with snow and sodium chloride solution 1 per 

 cent., a fluid is obtained which on filtering is at first liquid, but will finally 

 clot; the clot is myosin. 



Myosin, on addition of dilute acids, dissolves and forms syntonin or 

 acid-albumin. It is less soluble in dilute saline solutions than (c] and 

 (d). It coagulates at 55 60 C. 



