152 ANATOMY FOR NURSES [Chap. IX 



Intravascular clotting. — It is well known that clots occasionally 

 form within tlie blood-vessels. The most frequent causes are : — 



(1) When the internal coat of a blood-vessel is injured, as for 

 instance by a ligature, the endothelial cells are altered and may 

 act as a foreign substance. If in addition there is a stasis of 

 blood at this point, disintegration of the blood-plates and white 

 corpuscles may result in the formation of thrombin and a clot. 



(2) Any foreign material, even air, that is introduced into the 

 blood and not absorbed may stimulate the formation of thrombin 

 and a clot. 



Thrombus and embolus. — A clot which forms inside a blood- 

 vessel is called a thrombus. A thrombus may be broken up and 

 disappear, but the danger is that it may be carried to some point 

 in an important vessel where it acts as a wedge, blocks circulation, 

 and may cause instant death. A thrombus that becomes dislodged 

 from its place of formation is called an embolus. 



Regeneration of the blood after hemorrhage. — A large portion 

 of the total amount of blood in the body may be lost suddenly by 

 hemorrhage without producing a fatal result. It is probable 

 that a healthy individual may recover from the loss of as much as 

 three per cent of the body weight, provided the lost blood is at once 

 replaced by a solution having the same degree of concentration, 

 and containing one or more of the important salts of the blood. 

 Physiological saline solution, ?'.<?., sodium chloride 0.7 to 0.9 per cent, 

 fulfills these conditions, and is usually introduced directly into a 

 vein. This operation is called intravenous infusion, and the bene- 

 fits derived from it are : — 



(1) The heart-beat is increased, because it must make stronger 

 contractions to propel the extra fluid. 



(2) The volume of the circulating fluid is sufficiently increased 

 to maintain normal conditions of pressure and velocity. 



(3) The red corpuscles are kept in rapid circulation and thus 

 loss of oxygen to the tissues is prevented. 



(4) The tissue cells are provided with water and thus protected 

 from the bad effects that would follow the withdrawal of water. 



Plasma is regenerated with some rapidity but it may take 

 days or even weeks before the number of red blood corpuscles 

 and the haemoglobin gets back to normal. 



