V.] THE BLOOD. 39 



albumin is precipitated. Sodic sulphate alone, however, gives no 

 precipitate with pure serum. 



18. Precipitation of Serum Proteids by Other Salts. 



(a.) Precipitate blood-serum with potassic phosphate. All the proteids are 

 tin-own down after prolonged shaking. 



(l>.) Precipitate blood-serum with magnesic sulphate and sodic sulphate, or 

 the double salt sodio-magnesic sulphate. All the proteids are thrown down. 



19. Coagulation Temperature of Serum-Proteids. Saturate 

 sernm with MgS0 4 . Filter, keep the nitrate, label it B. Wash 

 the precipitate, i.e., the serum-globulin with saturated solution of 

 magnesium sulphate until the washings give no reaction for albu- 

 min. This takes a long time, and had better be done previously 

 by the demonstrator. Dissolve the precipitate in distilled water, 

 which gives an opalescent solution. Label it A. Acidify it 

 slightly with a drop of 2 per cent, acetic acid, and determine the tem- 

 perature at which it coagulates by the method stated on p. 11. 

 The liquid in the test-tube should just cover the bulb of the 

 thermometer. Coagulation takes place about 75 C. 



The nitrate B contains the serum-albumin. Dilute it with an 

 equal volume of water, faintly acidify and heat, as above. A pre- 

 cipitate falls about 77-79 C. (B), and on filtering this off, and 

 again acidifying, another precipitate is obtained on heating to 

 84-86 C. 



20. Preparation of Fibrinogen from Hydrocele Fluid, which 

 does not coagulate spontaneously. 



(a.) Dilute 10 cc. of hydrocele fluid with 150 to 200 cc. of water, and pass 

 through it for a considerable time a stream of carbon dioxide, when there is 

 precipitated a small quantity of a somewhat slimy white body, fibrinogen. 

 (Schmidt's method.) 



(b.) Half saturate hydrocele fluid with sodium chloride solution 

 by adding to it an equal volume of saturated solution of sodium 

 chloride. Fibrinogen is precipitated in small amount. Filter, and 

 on adding MgS0 4> serum-globulin is precipitated, so that hydrocele 

 fluid contains both fibrinogen and serum-globulin. 



21. Coagulation Experiments. 



(a.) Andrew Buchanan's Experiment. Mix 5 cc. fresh serum 

 (preferably from horse's blood) with 5 cc. hydrocele fluid and 

 keep the mixture at 35 C. for some hours, when coagulation occurs, 

 a clear pellucid clot of fibrin being obtained. Coagulation takes 

 place, and is due to the action of fibrin-ferment on fibrinogen and 

 not to the presence of serum-globulin, as hydrocele fluid in -addition 

 to fibrinogen contains this body. 



