AND BLOOD PRESSURE 167 



its original value, and the pressure fell from 117 to 37 mm. Hg. 

 On. bleeding the rabbit 12 c.c. and then 20 c.c., and then again 

 another undetermined amount, the pressure rose and reached 40 

 mm. Hg some twenty minutes after the first signs of cardiac failure. 

 At the end of another twenty minutes it had risen to 79 to 8G 

 mm. Hg. 



It is possible that the cardiac failure may be due in part to 

 other causes than the mere mechanical overloading of the heart. 

 Some experiments made by Bier seem to show that defibrinated 

 blood has a toxic influence, for he found that if he transfused the 

 excised limb of a pig with pig's blood, defibrinated and oxygenated, 

 at arterial pressure, an active hypersemia ensued at first, and the 

 blood flowed from the veins in a full stream. Soon, however, the 

 outflow diminished and became very small, and the limb turned 

 deep blue in colour. Arterial blood transfused directly into the 

 limb from another pig had no such effect ; the limb at each trans- 

 fusion became hypersemic for a time and then returned to its 

 natural colour. 



Worm-Muller observed that bleeding an animal, to the extent 

 only of that amount of blood which had been injected, killed it, 

 if the transfusion had been a large one. The excess of blood fluid 

 in part pooled in the expanded capillary-venous system and in 

 the tissue spaces, in part excreted, could not be drawn on quickly 

 enough to maintain an adequate supply to the heart. 



Much has been made of the increased resistance which is said 

 to occur in plethora owing to transudation and excretion of the 

 blood fluid and the concentration of the corpuscles. To the 

 greater viscosity so produced the overstrain and failure of the 

 heart has been attributed. The researches on surviving organs 

 show on the whole the same proportion between viscosity and 

 flow, as in a glass viscometer. If the viscosity is increased 

 50 per cent, the flow will be about 50 per cent, slower. Such 

 an alteration of viscosity is, however, of little significance in the 

 vascular system, for a slight excitation of the vaso-motor nerves 

 can alter the flow 100 per cent, or more. In the chewing muscles 

 of the horse the flow may increase four times or more during work 

 owing to vaso-dilatation and the furthering of the blood flow by 

 the alternate relaxation and contraction of the muscles. A drug 

 such as Yohinbim may in the first stage of its action lessen flow 

 50 per cent, and pressure 18 per cent., and subsequently increase 



