595 



Comment on papers 57 — 59 



In ourfirst determination of the erythrocyte volume in 1940 we availed ourselves of 

 the blood of a rabbit injected with ^-P a few days previously. A known aliquot 

 of the blood of this rabbit was then injected into a receptor rabbit. At different 

 times after injection, the activity of the total acid-soluble P extracted from an 

 aliquot of the receptor blood was compared with the corresponding activity 

 of the same aliquot of the donor blood. In some of the experiments not the activ- 

 ities of the acid-soluble fractions but those of the phosphatide fractions were com- 

 pared. The device described (paper 51) necessitates the availability of a donor and 

 thus could not be applied in clinical red corpuscle volume determinations. We, 

 therefore, replaced, in 1942 the above procedure by an improved one in which the acid- 

 soluble phosphorus compounds present in the erythrocytes are tagged in the course 

 of incubation of blood at body temperature for 1 — 2 hr, and a known volume of 

 this blood containing tagged erythrocytes is then reinjected into the circulation 

 (paper 58). Within the first 10 min after injection, which under physiological 

 conditions amply suffices to carry out a determination, of the red corpuscle volume, 

 the loss of 3-P by the injected human red corpuscles is insignificant ; after the lapse 

 of 1 hr the loss is about G per cent. We injected in our studies labelled whole blood 

 to compensate the small ^ap by a corresponding incorporation of plasma 

 32P into the circulating erythrocytes (paper 52). Later, mostly labelled red 

 corpuscles suspended in inactive plasma or saline were injected in such deter- 

 minations. Comparing the results obtained when injecting whole blood or suspended 

 erythiocytes, no significant difference was found by Hans Bohr (1954). ^^p {^ 

 vitro tagged erythrocytes found a very extended application in the forties and 

 the early fifties. At present, radiochromate labelled erythrocytes are mostly 

 applied in the determination of red corpuscle volume. The most extensive clinical 

 application of ^-P tagged red corpuscles starting at a very early date is due to 

 Nylin. ^-P labelled red corpuscles found also application in his recent studies 

 on brain circulation 



In vivo labeUing of erythrocytes through incorporation of radio-iron into their 

 haemoglobin was introduced by Hahn et al. (1941), thus soon after the first appli- 

 cation of in vivo ^-P labsUed erythrocytes in blood volume determiiiations 

 (paper 51). Radio-iron in vivo tagged erythrocytes proved to be very useful in 

 animal experiments, but were not suitable for clinical application (since they 

 necessitated a ^^Fe activated donor). 



Also *-K labelled erythrocytes found application in red corpuscle determinations 

 (paper 58). ^-K labelling of red corpuscles in vitro takes place about as rapidly 

 as that of ^^p labelling. ^'^K is retained better, and as its life-time is about thirty 

 times shorter than that of ^^P, a hum^m subject is exposed, after injection of ^^K 

 labelled erythrocytes, to a smaller radiation dose than after injection of ^^P label- 

 led red corpuscles of the same activity. The disadvantage of the method is 

 that fresh ^-K must be procured about every second day. An isotope with a still 

 shorter life-time than ^^K is the lead isotope ThB. By letting an oxygen stream 

 strike a radio-thorium sample, the former carries gaseous thoron given off by 

 radio-thorium. The thoron having a half-life of 56 sec only decays to an appre- 

 ciable extent when passing a blood stream producing ThB, which is almost quanti- 

 tatively taken up by the erythrocytes (paper 53 and Alexander, 1953). Activation 



38* 



