] 54 ADVEXTURES IN RADIOISOTOPE RESEARCH 



DETERMINATION OF THE RADIOACTIVE SODIUM PHOSPHATE 



The radioactivity of the samples of blood, bones, etc. to be analysed 

 is in most cases too feeble to be measured even by means of a very 

 sensitive electroscope. Geiger-Mijller counters, much more sensitive 

 instruments, are therefore utilised for measuring purposes. We use for 

 the most part tubes having an available surface of about 1.5 cm^. The 

 sample to be measured must accordingly be spread over about the same 

 area. The j^-rays emitted by the radio phosphorus are fairly penetrating 

 and are not much weakened when an aluminium dish of 1.5 cm^ 

 surface is filled to a depth of a few millimeters with a bone sample 

 weighing 100 mgm. We want to know what percentage of the radio- 

 active phosphorus taken is to be found after a certain time in, for exam- 

 ])le, the bones. The procedure is as follows. We take a solution of active 

 sodium phosphate, use 99 per cent of it for feeding the animal and keep 

 1 per cent as a "standard". We kill the animal, separate a bone sample, 

 ignite it, and measure its activity. Should the latter be, for instance, 

 half as large as that of the standard which is measured simultaneously, 

 then we can conclude that 0.99x0.5 per cent of the active phosphorus 

 atoms eaten are actually present in the bone sample investigated. 

 Although the jS-radiation from radioactive phosphorus atoms is not 

 rauch weakened in penetrating through 100 mgm of bone ash, 

 we can entirely eliminate the possible error due to this absorption by 

 adding 100 mgm of calcium phosphate to the standard solution; 

 this has the same absorbing power as the bone sample. It is advisable 

 to make the standard as similar to the sample to be measured as possible. 

 In dealing with urine, faeces, muscles, liver etc. we first destroyed the 

 organic matter by one of the usual methods; in several cases, however, 

 these were replaced by treatment with fuming nitric acid. Then calcium 

 phosphate and calcium oxide were added if necessary to make the sample 

 more similar in its composition to our standard preparation and finally 

 the sample was ignited. 



To demonstrate the utility of the isotopic indicator method we 

 will first consider the problem of the origin of the phosphorus in 

 the faeces. 



ORIGIN OF THE PHOSPHORUS IN THE FAECES 



Chemical analysis enables us to determine the phosphorus content 

 of the excreta but not to decide to what extent the phosphorus found 

 in the faeces is undigested material and what fraction of it is phosphorus 

 having its origin in the organism. The investigations described in this 

 paper have revealed that a fairly rapid interchange takes place between 



