( 395 ) 



coiicentralioiis of Uie siiine osiiiolic pressure iis llic luilural nicdiuiii 

 of the cüniCti aii<l coiijinietiva, iiainely the laclirymal fluid. 



Until now, liowevei', liiis pressure liad nol been ujcasured, at any 

 rate bv a (Hreet method, probably on account of the difficulty of 

 obtaining a (piantity of that fluid, sufficient for the customary methods, 

 viz. the freezing-point and the blood cor))uscles method. 



So I tried to find a method with which Vs ^'C., if necessary V^ ^'^^ 

 of liquid should be sufficient. T succeeded in finding such a method. 



It is based on the already known principle that the volume of 

 blood corpnscles is greatly dependent on the osmotic pressure of the 

 solution containing them. ^) 



This principle has I)cen applied here in the following manner. 

 The fluid to be examined is put into a small, funnel-shaped glass 

 tube, the cylindrical neck of which is formed by a calibrated capil- 

 lary, closed below. ") Let this quantity be \^^ cc. Into other similar 

 funnel-shaped tubes of the same size are put solutions of Na CI of 

 different concentration (0.8 "/„, 0.9 »/„, 1 "/„, 1.1 7„, 1.2 "/„, 1.3 "/„, 

 l-4°/„, 1.5 7„, 1.6 7J and to each of these 0.02 cc. of blood is 

 added. After half an hour — during which time the corpnscles are 

 sure to have found osmotic equilibrium with their surroundings — 

 the tubes are centrifuged until the sediments no longer alter their 

 volumes. It is obvious that the osmotic pressure of the fluid under 

 examination will be equal to that of the Na 01 solution in which 

 the sediment of blood corpuscles is the same as in the fluid examined. 

 We passingly remark that tliis solution of Na 01 in the case of 

 lachrymal fluid contained 1.4 Vo- 



A few remarks must be added. 



Firstly it may be asked whether the blood which is added to the 

 fluid to be examined does not appreciably alter the osmotic pressure 

 of that fluid. 



Assuming that the blood used contains 60 pOt. of serum, 0.02 cc. 



of blood will contain 0.012 cc. of serum. If the quantity of fluid 



was 1/2 cc, the total quantity of fluid will now be 0.012 -|- 0.5 = 



0.512 cc. If the fluid to be examined had an osmotic pressure of 



a 1.2 pOt. Na 01 solution and the serum that of a 0.9 pOt, Na 01 



solution, dilution of the fluid with the serum will have produced a 



0.012 X 0.9 4- 0.5 X 1.2 

 liquid with an osmotic pressure oi =1.19 pOt. 



NaOl. The osmotic pressure of the fluid is consequently reduced 



1) Hamburger, Gentralblatl f. Physiologic, 17 Juni 1893. 



*) Hamburger Jouiual de Physiol, norm, et palhologique 1900 p. 889. 



