700 EEPORT— 1903. 



the monometer only. Thus the initial reading of the mercurial monometer gives 

 the zero pressure, and subsequent readings at different time intervals after the 

 commencement of the experimnet give the osmotic pressure. 



The instrument lias been used, up to the present date, with solutions of gela- 

 tine, .starch, and gum acacia. 



The experiments with gelatine sbow that the colloid can be used for experi- 

 mentation in this osmometer without undergoing change for prolonged periods. 

 Thus in one experiment which was carried on for eighty-six days the gelatine was 

 recovered at the end as a clear jelly, setting at 21°-22° C, which showed no signs 

 of alteration from that which was originally placed in the osmometer. Even after 

 such a prolonged dialysis the pressure obtained at the end was, at the same tem- 

 perature, the same as that at the beginning of the experiment. This proves that 

 the pressure is not due to any diffusible crystalloid, which would have been 

 equated by dialysis, but is produced by the dissolved colloid. ' 



The figures for the osmotic pressure at a temperature of 40° C. give for the 

 molecular weight in solution, or solution aggregate, of gelatine 18,600, which is 

 of the same order of magnitude as the solution aggregates of various forms of 

 proteid. 



3. Experiments on the Permeability of Lipoid Membranes, 

 By Professor Benjamin Moore, M.A., D.Sc. 



The theory has been enunciated by Overton that the osmotic properties of 

 the cell are due to substances termed lipoids, such as cholesterin and lecithin in 

 the cell membrane, which are supposed to be impermeable to certain crystalloids 

 such as sodium chloride, but freely permeable to water. So that these bodies act 

 as semi-permeable membranes, and hence give rise to the osmotic phenomena 

 shown by cells. 



The theory has been extended by Overton and by Friedenthal to explain other 

 important phenomena such as anesthesia and fat-absorption by assuming that the 

 lipoids act as solvents, and take up into the cell the anossthetics and fatty bodies. 



Admitting that fats and anaesthetic substances are readily soluble in lecithin 

 and allied bodies, it is difficult to see why these substances should be given up 

 again from these lipoids to the active protoplasmic constituents of the cell; and, 

 further, there is no experimental proof that every cell is surrounded by such a 

 lipoid membrane. 



But such an extensive use has been made of the theory which has received con- 

 siderable credence that it appeared desirable to test whether membranes composed 

 of such substances possess the properties which have been assigned theoretically 

 to them. 



Accordingly the osmometer described in the previous paper has been used for 

 this purpose. 



Membranes saturated with lecithin and lanoline have been employed, using 

 sodium chloride solutions of dill'erent strengths on the two sides of the membrane, 

 and also sodium chloride solution against distilled water. It has been found that 

 such membranes are distinctly permeable to sodium chloride, as well as distilled 

 water, and that no appreciable osmotic pressure is developed, showing that the 

 osmotic phenomena of the cell are not due to such membranes, and that such 

 membranes, If they did exist, furnish no explanatlou of the absorptive properties of 

 the cell or of the phenomena of antesthesia. 



4. Tlie CerebrtLm of Aj^es} 

 By Professor Sherrington, F.B.S., and A. S. GrOnbaum, M.D. 



5. The Origin of Water in Saliva. By Joseph Barcroft, M.A., B.Sc. 



To be published in the Journal of Physiology, 



