RATE OF PASSAGE OF WATER THROUGH CAPILLARY AXD CELL WALLS 439 



20 sec. after all the heavy w^ater was injected. In the course of such a short time 

 as 40 sec, 644 cc. of the body water took part in diluting the heavy water injected 

 and, after the lapse of 24 min., as much as 1825 cc. 



The plasma water cannot diffuse into the cells without passing the capillary 

 waU. If the last mentioned process took place within 40 sec, then the volume 

 of the diluting water should be at least equal to that of the extracellular fluid 

 which amounts, in a rabbit weighing 2.6 kgm, to 670 cc('^^ As seen in column 4, the 

 volume of the diluting water was only shghtly less, namely 650 cc, than this 

 value. The total water content of the rabbit amounts to 70 to 75 per cent of its 

 weight, corresponding to a volume of 1820 to 1950 cc. As seen in column 4, the 

 sample collected after the lapse of 24 min was found to be diluted by 1825 cc. 

 body water. Within that time, therefore, a distribution of the heavy water in 

 almost the total body water took place, though some of the water present in cer- 

 tain organs may not have taken part in the exchange process(2) This point can 

 only be settled by investigating the density of tissue water. The above figures 

 suggest that, in contradistinction to a very fast invasion of the interspaces, the 

 penetration into the cells is a somewhat slower process. 



In the samples collected shortly after the start of the experiment the dilution, 

 due to a loss of heavy water by the body, can be disregarded. This is not the case 

 in experiments lasting several hours or days. In the course of 5 days, for example, 

 the loss of water through the kidneys alone amounts to about 1 hter, thus to 

 38 per cent of the rabbit's weight. In this case, the excretion of a corresponding 

 part of the heavy water is responsible for the, at first sight puzzhng, value of 109 

 per cent found. Some of the hydrogen atoms bound to oxygen or nitrogen in the 

 various organic compounds present in the body, exchange with those present 

 in the water or heavy water molecules, and this process will also increase the 

 dilution figures observed, as a removal of deuterium acts in the same way on the 

 water density figures as does dilution by normal water. In view, however, of the 

 fact that the amount of hydrogen present in the organic compounds is small 

 compared with that of the hydrogen incorporated in water molecules, the process 

 mentioned above will not much influence the dilution figures obtained. In experi- 

 ments of long duration, a successive replacement of most of the hydrogen atoms 

 present in organic molecules wiU take place, giving an additional outlet to some 

 of the deuterium atoms present in the body water. The percentage of hydrogen 

 present in the fats of the body which exchanges within I hour with water hydrogen 

 is neghgible; the corresponding amount of protein hydrogen is not (Ussing, 1938). 

 The water equivalent of this hydrogen amounts, however, only to 14 ^^ 2 per 

 cent of the body weight, or 13 to 52 cc. in the case of rabbit A and 8 to 30 cc. 

 in the case of rabbit B. The amount of cataboUc water formed in the course of 1 

 hour in the rabbits amounts only to about 0.1 per cent of the body weight. As 

 seen in Table 1, after the lapse of 39 days, the density excess of the blood water 

 very much declined. This dechne is mainly due to loss of the heavy water and, 

 thvis, of a corresponding amount of normal water present at the start of the expe- 

 riment in the body. About 5/6 of these molecules was lost in the course of 39 

 days. In the case of human subjects, who drank heavy water, it was found (Hevesy 

 and HoFER, 1934) that, in the course of 9 days, half of the heavy water taken 

 was lost. 



In the above connection, it is of interest to recall the experiments carried out 

 by McDouGALL, Verzar, Erlenmeyer and Gaertner (1394). They injected 



^1^ Comp., for example, A. Krogh (1937). 

 ^2>Comp. UssiNG (1938). 



