REFERENCES - 209 



poration of C^^ into the free carboxyl groups of the amino acids in Hver 

 protein hydrolysates was observed by Hempelmann (94) after adminis- 

 tration of carboxyl-labeled alanine to mice. 



Not all differences found in the rate of C^^ incorporation due to ir- 

 radiation are to be explained by a change in the sensitivity of the radio- 

 active indicator. For example, because of decreased rate of incorpora- 

 tion of glucose into liver glycogen of the irradiated guinea pig, as found 

 by Lourau (131, 132), less glucose C^* is expected to be incorporated 

 into liver glycogen in the irradiated animal. 



The application of C^^ as an indicator reveals a great variety of in- 

 direct effects. Interference with the normal steps of the Krebs cycle 

 in the liver may lead to a changed activity level of the circulating CO2, 

 which may reflect itself in the extent of C^^ incorporation into muscle 

 glycogen. Interference with the formation rate of labeled liver protein, 

 due to changes in the sensitivity of the indicator or to changed turn- 

 over rate, w ill influence the C^* content of plasma proteins and of proteins 

 of organs which take up proteins from the plasma. Acetoacetate, which 

 is one of the main fuels of muscle metabolism, is not synthesized in 

 that tissue (91) but is presumably carried into the muscle cells from the 

 liver or the intestinal mucosa. The effect of irradiation on the last- 

 mentioned organs must therefore reflect itself in the extent of C^* in- 

 corporation into muscle constituents. We meet here a great variety of 

 indirect effects of irradiation, some of which are discussed on p. 197 and 

 in H. Jones's paper. 



The mapping out of a metabolic route by the use of C^* as an in- 

 dicator is an arduous task. The task will be even more arduous if the 

 effect of irradiation on this route is to be elucidated. Changes produced 

 in one organ may be reflected very markedly in reactions taking place 

 in another organ. Changes in hormone production produced by irradi- 

 ation may, furthermore, exert a pronounced influence on metabolic path- 

 ways. In spite of these facts, the application of C^"* to radiation studies 

 may open a profitable line of attack. 



REFERENCES 



1. Lasnitzki, I., Brit. J. Radiol, 21: 265, 1948. 



2. Henshaw, P. S., Am. J. Cancer, 33: 258, 1938. 



3. Loveless, A., and S. Revell, Nature, 164: 938, 1949. 



4. Bullough, W. S., /. Exptl. Biol, 26: 261, 1949. 



5. Bullough, W. S., Nature, 165 : 493, 1950. 



6. Roberts, R. B., and J. E. Roberts, /. Cellular Comp. Physiol, 36: 15, 1950. 



7. Medawar, P. B., Quart. J. Microscop. Sci., 88: 27, 1947. 



8. Runnstrom, J., Biol Bull, 68: 327, 1935. 



9. Brachet, J., Arch, biol, 46: 1, 1934. 



