336 PRACTICAL PHYSIOLOGY 



(4) Contact with a rough surface (cf. effect of receiving into oil). 



(5) Addition of calcium salts. 



(6) Intra-mtam methods causing blood to clot within the vessels : 



(a) Injury or death of blood-vessel wall. When an artery is crushed, 

 as in a contused or lacerated wound, a clot forms, which acts as a 

 natural plug to prevent haemorrhage. When the arterial wall under- 

 goes degeneration a clot or thrombus, as it is termed, may form. 

 Similarly, when a blood-vessel is ligatured the inner coat is injured, 

 and a clot forms for a short distance from the ligature. This clotting 

 is due to the liberation of thrombokinase from the injured tissues, 

 causing the formation of some thrombin. That the clot does not extend 

 indefinitely in the blood is due to two causes : (a) thrombin is adsorbed 

 into the fibrin it precipitates ; and (b) the formation of anti-thrombin. 



(b) Rapid injection into a vein of a strong alkaline solution of 

 nucleo-protein ; the so-called " positive phase" of nucleo-protein injection. 



Preparation of Fibrin Ferment. Blood serum, or some defibrinated blood, 

 is mixed with twenty times its bulk of alcohol. A copious white precipitate is 

 obtained. Allow this to stand under the alcohol for two months. By this time 

 all the other proteins present will be coagulated, except fibrin ferment. The 

 fluid is pipetted off, the sediment carefully collected on a filter, and after the 

 alcohol has drained off ground up in a mortar with water. This extracts the fibrin 

 ferment. Filter, and keep filtrate. 



BLOOD SERUM. 

 Proteins. EXPERIMENT VI, Divide into three portions a, b, c. 



(a) Allow a to drop gradually into a beaker filled with distilled water; 

 a cloud forms round each drop as it mixes with the water. This is due 

 to the precipitation of the globulin present, as there is now too little 

 saline present to keep it in solution. 



(b) Saturate b with crystals of magnesium sulphate ; a precipitate of 

 globulin occurs. Filter. Show that the filtrate contains albumin (i) 

 by faintly acidifying with acetic acid and heating in a water bath note 

 the temperature at which the albumin coagulates (77-79 C.) ; (ii) fully 

 saturating the solution with ammonium sulphate. 



Redissolve the precipitate of globulin in water ; faintly acidify and 

 note the temperature of heat coagulation (75 C.). 



(c) To c add an equal amount of fully saturated Am 2 S0 4 (half 

 saturation). The globulin is precipitated. Filter and fully saturate 

 (add solid crystals) with Am 2 S0 4 ; a precipitate of albumin results. 



Salts. 



EXPERIMENT VII. Faintly acidify the serum and boil to coagulate 

 the proteins. Filter. Test the filtrate for : 



