V.] THE BLOOD. 37 



15. Defibrinated Blood. In a slanghter-house allow the blood 

 from an animal to run into a vessel, and with a bundle of twigs 

 beat or whip the blood steadily for some time. Fine white fibres 

 of fibrin collect on the twigs, while the blood remains fluid. This 

 is defibrinated blood, which does not coagulate spontaneously. 



16. Fibrin. Wash away the colouring-matter with a stream of 

 water from the twigs until the fibrin becomes quite white. 



(a.) Physical properties : it is a white, fibrous, elastic substance. 

 Stretch some fibres to observe their extensibility ; on freeing them, 

 they regain their shape, showing their elasticity. 



(b.) Place a few fibres in absolute alcohol to rob them of water. They 

 become brittle and lose their elasticity. 



(tf.) Place a small quantity of fibrin in a test-tube with some 

 0.2 per cent, hydrochloric acid in the cold. It swells up and 

 becomes clear and transparent, but does not dissolve. 



(d.) Repeat (c.), but place the test-tube in a water-bath at 60 C. ; part of 

 the fibrin is dissolved, forming acid-albumin. Test for the latter (Lesson I. 7). 



(e.) Place some hydric peroxide over fibrin in a watch-glass; 

 bubbles of oxygen are given off. Immerse a flake in freshly- 

 prepared tincture of guaiacum (5 per cent, solution of the pure resin 

 in alcohol), and then in hydric peroxide, when a blue colour is 

 developed, due to the ozone liberated by the fibrin striking a blue 

 with the resin. If the fibrin contains much water, it is preferable 

 to place it first of all for a short time in rectified spirit to remove 

 the water. [Other substances give a blue colour under similar 

 conditions ] 



(/.) Place some fibrin in water in a test-tube. Note that it gives the 

 xanthoproteic reaction and Millon's test (Lesson I. 1). 



((/.} Prick a finger with a needle, collect a drop of blood on a microscopic 

 slide, cover, and examine under a microscope ( x 350). After a time, observe 

 the formation of threads of fibrin between the rouleaux of coloured blood- 

 corpuscles. 



17. II. Blood-Serum. By means of a pipette remove the serum 

 from the coagulated blood or siphon it off (Lesson V. 8). If a 

 centrifugal apparatus is available, any suspended blood-corpuscles 

 can easily be separated by it. Note its straw-yellow colour and 

 musky odour. Its reaction alkaline. Its sp. gr. = 1034. 



General Proteid Reactions. 



(a.) Dilute i volume of serum with 10 volumes of normal saline 

 or salt solution. 



(b.) Test separate portions by neutralisation and heat = coagu- 

 lation ; nitric acid and the subsequent addition of ammonia ; acetic 



