"THORIUM B" IX BLOOD VOLUME STUDIES 581 



cuvette, or in dry state, with that of a sample secured after injection, 

 in order to arrive at a correct figure for the circulating ])lood volume 

 of the patient. 



The present communication describes a method of blood volume 

 determination which fulfills to some extent the above conditions. It is 

 based on an observation^^^ that when oxygen carrying thoron is led 

 through a blood sample, an appreciable part of the thoron decays within 

 the sample, and its decay product thorium B (ThB) is almost entirely 

 taken up by the corpuscles, from which it is released at a very slow 

 rate.* 



METHOD 



Radio-thorium preparations are easily available. We applied a sample 

 prepared according to the Hahn procedure and having the activity of 

 2 mgm of radium. It was obtained (price £7 per mihicurie) from Harwell. 

 Such a preparation is a copious source of thoron gas (thorium emanation). 

 It is placed in a small glass vessel of a weighing glass type. Through the 

 stopcock of the vessel two narrow glass tubes are inserted: through one, 

 oxygen is led into the vessel, through the other, the thoron-loaded 

 oxygen is led (for example, for 10 minutes) into the blood sample to 

 be activated. The narrow glass cylinder containing the blood sample is 

 placed in a small wash bottle. Since rubber strongly absorbs thoron, 

 rubber tubing is kept at a minimum. 



Thoron absorbed by the blood sample decays with a half-time of 55 

 seconds and is converted into ThB and its disintegration products. 

 Within five minutes, all thoron absorbed by the blood decays, and the 

 activity of the blood sample is now exclusively due to the presence of 

 ThB and its disintegration products, the activity of ThB decaying with 

 a half-time of 10.6 hours. 



While the larger part, 10 ml, for example, of the active blood sample 

 is reinjected into the human subject, whose blood volume we wish to 

 determine, a small fraction is applied to prepare a standard sample. 

 In preparing such a sample, we add, for example, 0.02 gm of active 

 blood to 2 gm of inactive blood (or saline), hemolyse the sample by 

 adding a few grams of saponin, and pour the hemolysed blood into one 

 of Zerahn's cuvettes^^\ or preferably dry the sample and pour 100 mgm 

 of the dry sample into an aluminium dish 1.2 cm in diameter, or, if 

 a larger blood sample is available, preferably into a dish of larger diame- 

 ter. The activity of the standard sample is then compared with the 

 activity of a blood sample secured, for example, 10 minutes after the 



* The uptake of ThB by red cells was studied at an early date by Behrens 

 and Pachur [Arch. exp. Path. u. Pharmakol. 122, 319 (1927)]. 



