40 ELEMENTARY PHYSIOLOGY. [ill. 



a. Transfer with a pipette 2 or 3 c.c. of the 

 plasma into a small test-tube. Observe the 

 coagulation and compare it with that of 1. 

 Avoid shaking. Probably the fibrin will 

 adhere so strongly to the sides of the tube 

 that little contraction will take place. On 

 being freed from the glass it will contract. 

 If the clot has already shrunk away from 

 the sides of the vessel, it may since it is 

 colourless be overlooked unless the fluid be 

 carefully examined. 



I. Dilute 1 c.c. of the plasma with 50 c.c. of 

 distilled water or normal saline solution. 

 Carefully avoid shaking and leave it till 

 the next day. Observe the fine delicate 

 fibrils of fibrin which are formed. 



9. Examine the plasma of blood prevented from 

 coagulating by the presence of neutral salts 1 . 

 a. Remove 1 or 2 c.c. carefully with a pipette, 

 avoiding blood-corpuscles as much as possi- 

 ble, and dilute five to tenfold with water. 



filled with ice is placed in the one which receives the blood. Horse's 

 blood is preferable to bullock's or dog's, since it clots less readily and 

 the red corpuscles sink more quickly. 



1 In preventing coagulation by neutral salts, blood is collected in 

 a vessel containing a saturated solution of magnesic sulphate ; as the 

 blood runs in, it must be mixed well with the salt solution, preferably 

 by stopping the flow of blood now and then and turning the vessel 

 upside down. There should be about 1 vol. of the salt solution to 

 4 vols. of blood. The vessel may advantageously be surrounded by 

 ice or by ice and salt. On either method ( 9 or 10) clotting some- 

 times takes place, but the remaining fluid may still give a clot on 

 appropriate treatment. 



