388 



Prof. W. M. Bayliss. 



to note that the difference referred to is greater in the case of gum than in 

 the case of serum proteins or in that of gelatin. I take it that this is due to 

 the acid of the gum being a stronger one than those of the proteins, so that 

 its salts are more dissociated electrolytically. The difference in the case of 

 congo-red is still greater. 



The question is, then, Are we to take as the required colloidal osmotic 

 pressure of our ideal injection fluid, that against water or against Einger's 

 solution ? If the wall of the blood-vessels consists of a membrane permeable 

 to crystalloids, impermeable or nearly so to colloids, it will behave as the 

 parchment paper membrane of our osmometer, and we must take the 

 osmotic pressures as measured against Einger's solution as those which come 

 into play. We require a solution of a colloid which gives under these 

 conditions an osmotic pressure of about 40 mm. of mercury. This, as 

 Table II shows, is given by a 7-per-cent. solution of gum or a 6-per-cent. 

 solution of gelatin. As it happens, the viscosity of such solutions is only 

 very little higher than that of blood. If stronger solutions are used, water 

 is attracted from the tissues and the blood is diluted. This was actually 

 found to be the case when 8-per-cent. gelatin was injected. The viscosity of 

 a sample of blood taken immediately after the injection was 4 - 2 times that 

 of water; after an hour the viscosity had decreased to 3*4 times that of 

 water. 



As already pointed out, with equal cardiac output, the rate of blood flow 

 through the organs remains the same, although the arterial pressure may be 

 higher, if this rise of arterial pressure is due to increased peripheral 

 resistance from rise of viscosity. It might be thought that increased 

 viscosity is not desirable, since the work of the heart is increased thereby. 

 In practice, however, the output of the heart falls with a low blood pressure, 

 partly owing to insufficient inflow from the veins, partly owing to the heart 

 muscle suffering from deficient supply of oxygen. 



It is desirable, therefore, to increase both the viscosity and the colloidal 

 osmotic pressure of solutions used for intravenous injection after loss of 

 blood. This can be done effectively by the addition of 6 per cent, gelatin 

 or 7 per cent, gum acacia to Einger's solution. 



Loss of Vascular Tone. 



We pass on to those cases where the arterial pressure is low on account 

 of vascular dilatation, without diminution of the volume of blood in circu- 

 lation. This condition was obtained in my experiments either by dividing 

 the spinal cord at the foramen magnum, or by decapitation in Sherrington's 

 manner. It was 'found that, although solutions containing gum or gelatin 



