72 Dr Lazarus Barlow, On an Osmometer. [Feb. 10, 



Monday, February 10, 1896. 



Professor J. J. Thomson, President, in the Chair. 



Professor H. Marshall Ward, Sc. D., Christ's College, and W. H. 

 Duckworth, B.A., Fellow of Jesus College, were elected Fellows of 

 the Society. 



The following communications were made : 



(1) By Dr Lazarus Barlow. 



The author exhibited an osmometer designed for the estimation 

 of the initial rate of osmosis and a modification of the same suitable 

 for the examination of small quantities of fluids. The principle 

 of both is the same, viz. that the stem of the osmometer is kept 

 horizontal, and the level of the fluid inside the osmometer is the 

 same as the level of the fluid outside the osmometer. The larger 

 instrument is fully described in the Journal of Physiology, vol. xix. 

 1896, p. 140 and foil. ; the smaller instrument differs from it in 

 that it is immersed in water until the stem of the osmometer 

 just shows above the surface. By these instruments the author 

 found that the initial rates of osmosis are not indicated by their 

 final osmotic pressures, or in other words by their freezing points ; 

 thus, to give an example, with a copper-ferrocyanide membrane 

 the initial rate of osmosis of a decinorrnal solution of urea was 

 half as great again as the rate of osmosis of a decinorrnal solu- 

 tion of glucose, whereas urea and glucose being indifferent sub- 

 stances, decinorrnal solutions of each have the same freezing point 

 and the same final osmotic pressure. The object for which the 

 research was performed was to see whether it is justifiable to apply 

 deductions from the freezing point of fluids existing in the animal 

 body to the question of lymph formation. Since the freezing point 

 determinations give no indications as to the relative amounts of 

 osmosis of two solutions of different composition at pressures 

 possible within the animal body, i.e. approximately at atmospheric 

 pressure, application of the laws of osmosis which are true at final 

 osmotic pressures are not justifiable in the case of the animal body 

 where such pressures can at best but rarely occur. 



