COAGULATION OR CLOTTING 87 



chloride, iso tonic with the blood (0.9 per cent.) in man, is in- 

 jected into the veins. The salt solution increases the blood 

 pressure and makes effective the remaining blood corpuscles, 

 which in normal blood are always in excess of the number 

 absolutely required for respiratory purposes. 



The injection of saline solution into the bloodvessels of a 

 normal animal raises the blood pressure, but never above 

 180 mm. Hg. This limit holds true also when the pressure 

 has previously been lowered by hemorrhage or by section of the 

 cervical cord. The explanation of this fact lies in the manner 

 in which the heart is affected. As soon as the arterial tension 

 reaches its maximal height, the heart beats slower and less 

 vigorously, and the residual blood in the left ventricle increases. 

 This causes a diastolic rise of pressure in the ventricle, which 

 is propagated back through the left auricle, pulmonary circuit, 

 right heart, to the veins. There arises in this way a congestion 

 of the veins and capillaries of the lungs and abdominal organs 

 chiefly. An amount of salt solution equal to four times the 

 normal quantity of blood of the animal may in this way be 

 accommodated. The liver becomes hard, tense, and swollen, 

 and other tissues become edematous. Owing to the transuda- 

 tion of fluid, the body becomes dropsical. . The bladder is dis- 

 tended with urine, and the stomach and intestines become filled 

 out with fluid. These factors prevent the blood pressure from 

 rising much above the normal. After the injection the arterial 

 and venous pressures return quickly to the normal, generally 

 within an hour. Injection of saline solution differs from trans- 

 fusion of blood in that in the former case the blood flow is 

 accelerated. The solution injected must be isotonic with the 

 blood of the animal, of the same temperature, and every pre- 

 caution taken to prevent the entrance of air. When injection 

 of salt solution is maintained for some time, the work of the 

 heart is increased, and cardiac failure sometimes results. In 

 the endeavor to avoid the latter it has been found that blood- 

 letting rapidly reduces arterial pressure, but owing to a general 

 paralysis of the vasomotor apparatus through overdistention, 

 the animal is easily killed by the hemorrhage. One hundred 

 and fifty per cent, of the normal quantity of blood of the animal 

 is the maximal amount that can be injected without directly 

 endangering the life of the animal. 



