THORIUM B LABELLED RED CORPUSCLES 533 



of ThB. This radioactive body emits soft ^-rays, its disintegration pro- 

 ducts hard y5-rays. One of these ThC" emits, furthermore, very hard 

 y-rays. The approximate half- value thickness of the /5-rays emitted by 

 ThB and its disintegration products in aluminium is the following: 



ThB (lead isotope) 1.6 xlO"! ^m 



ThC (wismuth isotope) 1.2 mm 



ThC" (thallium isotope) 7.7xlO"i mm 



The half value thickness of the y-ray emitted by ThC" is 17 cm. 



As the ^-rays emitted by ThC have almost the same hardness as those 

 emitted by ^^p^ they are very conveniently measurable. 



In our experiment, a stream of oxygen after having brushed over the 

 surface of a racliothorium preparation of about 1 mC activity was led 

 through 4 ml of rabbit blood. Plasma and red corpuscles were then 

 separated, washed 2 to 3 times with inactive plasma and then shaken 

 with inactive plasma of the same rabbit for 2 hr at 37° in the ther- 

 mostat. 



Corpuscle and plasma samples were dried at 60° and 50 mgm of each 

 sample placed in an aluminium dish; their /5-activity was then determined 

 with the Geiger counter. We determined the water content of each cor- 

 puscle and plasma sample and could thus calculate from the activity 

 figures of the dry samples the activity of fresh plasma and fresh cor- 

 puscles. 



The thorium emanation penetrates rapidly into the red corpuscles. 

 It decays very rapidly as well and we soon find 1 gm of corpuscles to 

 contain twice or more of thorium-active deposit than 1 gm of plasma. 

 These figures depend on the velocity of the oxygen stream and on other 

 experimental conditions. Through decay of thoron thorium B is formed 

 in the plasma as well and a part of this thorium B is also taken up by 

 the erythrocytes. 



We found that after 2 hr shaking of active corpuscles with inactive 

 plasma the corpuscles contained 50,560 counts but the plasma contained 

 only 170. Thus the red corpuscles gave off only 0.34% of their activity 

 in the course of 2 hr. The maximum loss was shown by a corpuscle sample 

 containing 87,800 counts, with 403 counts in the corresponding plasma. 

 In this case the loss was 0.46%. 



All these activities were measured 24 hr after leading thoron into the 

 blood, thus after more than 2 decay periods of ThB have already elapsed. 

 Strong corpuscle activities can thus be obtained by leading thoron for 

 a few minutes only through a blood sample. 



That the erythrocytes so well retain their content of ThB and its 

 disintegration products is partly due to the fact that much of the active 

 deposit of thorium, present in the red corpuscles, is in a colloidal or protein 



