THE BLOOD. 0-L 



(4.) Chemical Composition of Fibrin. The part played by fibrin 

 in the formation of a clot has been already described (p. 58), and it is 

 only necessary to consider here its general properties. It is a stringy 

 elastic substance belonging to the proteid class of bodies. It is insoluble 

 in water and in weak saline solutions ; soluble in ten per cent solu- 

 tion of sodium chloride, it swells up into a transparent jelly when 

 placed in dilute hydrochloric acid, but does not dissolve, but in strong 

 acid it dissolves, producing acid-albumin x ; it is also soluble in strong 

 saline solutions. Blood contains only .2 per cent of fibrin. It can be 

 converted by the gastric or pancreatic juice into peptone. It possesses 

 the power of liberating the oxygen from solutions of hydric peroxide, 

 H 2 0, or ozonic ether. This may be shown by dipping a few shreds of 

 fibrin in tincture of guaiacum, and then immersing them in a solution 

 of hydric peroxide. The fibrin becomes of a bluish color, from its hav- 

 ing liberated from the solution oxygen, which oxidizes the resin of guai- 

 acum contained in the tincture, and thus produces the coloration. 



The Gases of the Blood. 



The gases contained in the blood are Carbonic acid, Oxygen, and 

 Nitrogen, 100 volumes of blood containing from 50 to 60 volumes of 

 these gases collectively. 



Arterial blood contains relatively more oxygen and less carbonic acid 

 than venous. But the absolute quantity of carbonic acid is in both 

 kinds of blood greater than that of the oxygen. 



Oxygen. Carbonic Acid. Nitrogen. 



Arterial Blood, . . 20 vol. per cent 39 vol. per cent 1 to 2 vols. 

 Venous " 



(from muscles at rest) 8 to 12 " " " 40 " " " 1 to 2 vols. 



The Extraction of the Gases from the Blood. As the ordinary air- 

 pumps are not sufficiently powerful for the purpose, the extraction of 

 the gases from the blood is accomplished by means of a mercurial air- 

 pump, of which there are many varieties, those of Ludwig, Alvergnidt, 

 Geissler, and Sprengel being the chief. The principle of action in all is 

 much the same. Lud wig's pump, which may be taken as a type, is rep- 

 resented in Fig. 77. It consists of two fixed glass globes, C'and F, the 

 upper one communicating by means of the stop-cock D, and a stout in- 

 dia-rubber tube with another glass globe, L, which can be raised or 

 lowered by means of a pulley ; it also communicates by means of a stop- 

 cock, B, and a bent glass tube, A, with a gas receiver (not represented 

 in the figure), A, dipping into a bowl of mercury, so that the gas maybe 

 received over mercury. The lower globe, F, communicates with by 



1 The use of the two words albumen and albumin may need explanation. The 

 former is the generic word, which may include several albuminous or proteid bodies, 

 e. g., albumen of blood; the latter which requires to be qualified by another word is 

 the specific form, and is applied to varieties, e. g.. egg-albumin, serum-albumin. 

 6 



