( 396 ) 



by O.Oi pCt Na CI by the addition of 0.02 cc. of seruiii, a difference 

 which cannot even be detected with the Beckmann apparatus. 



If instead of 1/2 cc. of fluid only 1/4 cc. has been used, a similar 

 calculation shows that the osmotic pressure of the fluid under exami- 

 nation is diminished by a 0.014 pCt. Na CI solution, corresponding 

 to a depression of scarcely 0.0084°, a difference of depression, 

 lying near the limit of accuracy of Beckmann's determination of the 

 fi-eezing point. 



However, if the difference were greater, this could be no objec- 

 tion to the method, since also the Na CI solutions are mixed with 

 the same quantity of blood. 



The second remarlv concerns the pipette and the tubes. 



In order to measure accurately, the bore of the pipette must be 

 narrow and accordingly the instrument itself long. The column of 

 0.02 cc. of blood has a length of 143 mm. The same remark applies 

 to the funnel-shaped tubes. The calibrated capillary part has a length 

 of 57 millimetres and a volume of 0.01 cc. and is divided into 

 100 equal parts, which can easily be observed with the naked eye, 

 fractions being estimated with a magnifying glass. 



The use of funnel-shaped tubes of the same length, but with a 

 still smaller volume of the capillary part than 0.01 cc, which 

 would enable us to make determinations of the osmotic pressure 

 of much smaller i|uantities of liquid than V4 <-*c., would give rise 

 to technical difficulties, on Avhicli I will not dwell here. No more 

 shall I mention here the special precautions in experimenting, neces- 

 sarv for obtaining accurate figures. This subject will be dealt with 

 elsewhere. 



In order to give an idea of the reliability of the method, a table 

 follows, containing two series of parallel experiments. (See p. 397). 



The agreement between the figures (each di\'ision represents 



-J z:= 0001 cc.) is seen to be very satisfactory. 



100 ■ ^ 



A third remark concerns the possibility of makiiig one or more 



additional determinations with the same fluid, for checking the 



result obtained. All one has to do is to drain off the liquid above 



the sediment by means of a finely drawn tube or pipette and to 



convey it into another funnel-shaped tube, to add agaiti 0.02 cc. of 



blood and to centrifuge in the same way. The liquids in the NaCl- 



tubes are treated in the same way. Undoubtedly one changes the 



osmotic pressure of the liquids a little by agaiii introducing 0.02 cc. 



of blood, but this is done with all the liquids and so the alteration 



