Methods of Raising a Low Arterial Pressure. 385 



and sometimes temporarily above this height. The explanation of this 

 latter fact will be seen immediately. Thus : — 



A cat with a blood pressure of 110 mm. of mercury had about half 

 of the calculated amount of its blood removed. The pressure fell to 40 mm. 

 It was brought back at once by the injection of an equal volume of Ringer's 

 solution containing gum in sufficient quantity to raise its viscosity to 3"1 

 times that of water. In the course of two or three minutes the pressure 

 rose further to 145 mm. Although it soon commenced to fall slowly, it was 

 still at its initial value of 110 mm. at the end of 43 minutes. It had only 

 fallen to 102 mm. in an hour and to 98 mm. in 75 minutes. Similar results 

 were obtained with gelatin. 



We see that by raising the viscosity of the injected fluid to that of blood 

 by the addition of gum or gelatin, the blood lost can be replaced by an 

 equal volume of the solution, with a return to its original height. Further, 

 that this height is maintained for an hour or so, and even then has only 

 fallen to an unimportant degree. 



Pure Ringer's solution, as shown above, is very inefficient in maintaining 

 the blood pressure even at that height to which it at first raises it. "Why 

 do gelatin and gum behave differently in this respect ? It is clear that 

 viscosity alone is not a sufficient explanation. The fact that gelatin solu- 

 tions caused a more permanent rise of blood pressure than pure saline was- 

 noted by J. Hogan and Martin H. Fischer (9), and Bogert, Underhill, and 

 Mendel (17) found that saline solutions containing 2 per cent, of gelatin 

 did not leave the blood-vessels as rapidly as pure saline. 



A partial explanation of these facts is given by Knowlton's experiments 

 on the secretion of urine (5). Starling (6) had shown that if the osmotic 

 pressure of the blood colloids, to which the membrane of the glomerulus is- 

 impermeable, be reduced by dilution of the blood, diuresis results. This is 

 the case when a pure saline solution is injected. But Knowlton showed 

 that by the addition of a colloid which has an osmotic pressure, such as 

 gelatin, the effect of the dilution is greatly decreased. Further, if a colloid 

 which has no perceptible osmotic pressure, such as the soluble starch used 

 by him, be added, instead of gelatin, the diuresis is as great as with saline. 

 This is confirmed by the following experiment : — 



A cat with a blood pressure of 180 mm. of mercury had one- third of its 

 blood removed. An equal volume of 5-per-cent. soluble starch in Binger'& 

 solution was injected when the blood pressure was 70 mm. It was brought 

 back, temporarily, to 160 mm., the viscosity of the solution being only 

 2 - 2 times that of water. The blood pressure then began to fall, becoming 

 130 mm. in 18 minutes, and 62 mm. in 40 minutes. At the end of the^ 



