PROGRESS OF THE ISOTOPIC METHODOLOGY 1009 



to 20 days. In spite of this fact the mice had an unchanged haemog- 

 lobin content as the increased rate of destruction was compensated 

 by an increased rate of formation if we only disregard a short interval 

 before death. That in the cancerous mouse erythrocytes arc synthetized 

 at a strongly enhanced rate is shown by Fig. 10. When labelled glycine 

 was injected to mice after tumour formation, about 4 times as much 

 i*C was incorporated into the haemin of the red corpuscles as in that 

 of controls. 



TRACING THE ORIGIN OF BODY CONSTITUENTS AND THE 



REACTION PATHS 



A very fascinating application of radioactive tracers is the locating 

 of the origin of body constituents and the study of the paths of reactions 

 taking place in the organism. 



One of the earliest applications of ^^p was the tracing of the origin 

 of the phosphatide molecules of the milk in order to find out if these 

 move from the plasma into the milk or are synthetized in the milk gland^^'\ 

 Labelled orthophosphate was administered to the goat and 4.5 hours 

 later the specific activity of the phosphatide P of the milk, plasma, milk 

 gland, liver and kidney was determined. x\s seen in Table 1 the milk 

 phosphatide phosphorus could not have originated from the plasma 

 phosphatides as the specific activity of the latter is much lower than 

 that of the former. A precursor can clearly not have a lower specific 

 activity than the product formed from the precursor if we are not in 

 that stage of the experiment in which the specific activity of the plasma 

 phosphatide has already decreased with time. This was not the case in 

 the above experiment, taking 4.5 hours only. Thus it follows from the 

 figures of Table 1 that the milk phosphatides were synthetized in the 

 milk gland. The specific activity of the milk phosphatides is lower than 

 that of the milk gland phosphatides. We cannot expect the milk phos- 

 phatides to have exactly the same specific activity as the milk gland 

 phosphatides, we can only expect them to be lower or equal. The phos- 

 phatides present in the milk are released at different times from the milk 

 gland and the milk released by the gland was partly built up at a time 

 when the ^^p activity level of the gland was very low or even absent. 

 The figures of Table 1 demonstrate also that the phosphatide synthesis 

 in the milk gland is going on at a more rapid rate than in the liver or 

 the kidneys, thus at a very rapid rate. 



Seymour Cohn's tracing of the origin of the phosphorus atoms of the 

 desoxyribonucleic acid, one of the main constituents of the virus investi- 

 gated, is a beautiful example of this type of application of radioactive 

 indicators^^*'"^^). In bacteria such as the Escherichia coli 80% of the total P 



64 Hevesv 



