The Cerebro-spinal Fluid in the Human Subject. 347 



The Influence of Straining and Posture on the Flow and Composition of the 



Fluid. 



In a monograph on the cerebral circulation* one of us (L. H.) put 

 forward the view that the rate of secretion of the cerebro-spinal fluid, 

 when the cranio-vertebral cavity is opened, depends directly on the 

 difference between the pressure in the cerebral capillaries and that 

 of the atmosphere. At the same time it was shown that cerebral 

 capillary pressure varies directly and absolutely with vena cava pres- 

 sure. Thus the cerebral capillary pressure can be raised with great 

 ease by any agency which causes a rise of pressure in the vena cava or 

 cerebral veins. On the other hand, cerebral capillary pressure varies 

 directly, but only proportionately, with aortic pressure, for between 

 the aorta and the capillaries there lies the peripheral resistance. 



It follows from the above that the easiest methods of raising the 

 cerebral capillary pressure in man are : 



(a) By compression of the abdomen. 



(b) By the assumption of the horizontal posture. In this position, 



however, the rise of venous pressure may be compensated by 

 the fall of arterial pressure, which normally occurs when the 

 body is at rest. This is, no doubt, the case during sleep. 



(c) By straining or forced expiratory effort, with the glottis closed. 



By all these methods the vena cava pressure is considerably raised ; 

 and by the last method the venous inlets into the thorax may be com- 

 pletely blocked, and the pressure in the cerebral capillaries raised to 

 something like aortic pressure. 



It is true that by such a forced expiratory effort the aortic pressure 

 is lowered. Nevertheless, the total effect on capillary pressure is a 

 very great rise, for a fall of aortic pressure of 25 mm. of mercury 

 produces a fall in cerebral capillary pressure of less than 5 mm. of 

 mercury, while a rise of vena cava pressure of 25 mm. of mercury 

 produces a rise of cerebral capillary pressure of 25 mm. Hg. 



The present case gave us a unique opportunity of testing the cor- 

 rectness of these views on the living human subject, and our experiments 

 entirely confirm them. As will be seen from the following figures, the 

 flow of cerebro-spinal fluid is accelerated by all those circumstances 

 which raise the cerebral capillary pressure. The increase in flow is, 

 moreover, accompanied by a decrease in the percentage of solid 

 matter. 



The experiments were conducted under the supervision of two of us 

 (StC. T. and L. H.) ; the chemical investigation of the fluid was. 

 performed, as before, by the third (W. D. H.). 



* ' The Physiology and Pathology of the Cerebral Circulation/ by Leonard Hill, 

 London, Messrs. Churchill, 1896. 



