RATE OF PASSA(iK OK WATER TlIKOroiI CAI'ILLAKY AXD CFA.L WALLS 441 



the cell walls, and vice versa. To this conclusion one may possibly object 

 that heavy water (D2O) may show a different behaviour from HgO and 

 recall the results obtained in the investigation of the rate of hemolysis 

 of erytrocytes of cattle and rats, which was found to take place about 

 44 per cent more slowly in DgO than in ILO (Parpart, 1935 ; Brooks, 

 1935). 



Contrary to tliose of the above mentioned authors, our experiments- 

 were not carried out with pure D^O but with very diluted heavy water, 

 the viscosity and other properties of which only slightly differ from 

 those of H.3O. Our most concentrated samples contained, in fact, less 

 than 2 per cent DgO, most of them containing very much less. The 

 DoO injected into the vein is diluted at once. The above mentioned 

 authors did not use heavy water as an indicator for water ; they were 

 interested in the differences shown by HgO and D2O when penetrating 

 into corpuscles. When heavy water is ussd as an indicator, it should 

 always be used in a state as diluted as possible, partly for the above 

 reasons and partly because such diluted solutions contain mainly DHO 

 which is very similar to H2O, while DgO is much less so. 



In view of the high speed of capillary passage found in our experiments, 

 it is of interest to calculate the time taken by the diffusion of water 

 molecules through the capillary spaces. The mean displacement t of 

 water in water is |/ 2 D (where D denotes the diffusion constant of water 

 in water, determined by using heavy water as an indicator), is 2 cm 

 per day (Okr and Thomson, 1935). Taking the size of the capillary 

 vessel as 20 f^, we arrive at the result that the displacement of water 

 molecules within that space takes 1 x 10^^ day, or about 7io sec, thus 

 an exceedingly short time. 



Summary 



Heavy water is injected into the vein of rabbits and blood samples taken at 

 intervals from the artery. The density of the water prepared from the blood samples 

 is determined and, from the density difference between the injected heavy water 

 and the blood water, the extent of dilution, which the heavy water molecules 

 experienced in the body at different times, calculated. 



As soon as a 14 min after the injection, a dilution of the heavy water by an 

 amount of body water corresponding in volume to about that of the extracellular 

 space of the body, is found. This very rapid rate of dilution is followed by a some- 

 what slower dilution process, in which the cellular water participates. 



After the lapse of less than % tour, the heavy water molecules are evenly 

 distributed over almost the total body water. 



After the lapse of 39 dajs, only about 1/5 of the heavy water injected is still 

 present in the bodj'. 



There is no reason to assume that the heavy water (mainly DUO) molecules 

 show a markedly different behaviour from that of the normal water (HgO) mole- 

 cules present in the body, and we have, therefore, to conclude thai within about 



