416 PHYSIOLOGICAL FACTORS IN MAMMALS 



rates, and none has been observed (1). Late changes of 90 per cent re- 

 duction in perfusion are apparent in mice that have been subjected to 

 comparable amounts of specific hver irradiation, but these are associ- 

 ated with cirrhotic changes in the liver such that there have been obvious 

 degeneration and regeneration of the tissue. 



With whole-body irradiation in the lethal range, there are disturb- 

 ances in coagulability of blood (5). Another disturbance in the com- 

 position of the blood at the lethal level of whole-body irradiation is the 

 development (in the rabbit) of an opalescence of the serum which is 

 apparently due to lipids smaller than chylomicrons and larger than the 

 usual lipid macromolecule. Such a lipemia is never present in the nor- 

 mal rabbit. Its development during the first 24 hr after irradiation 

 seems to be prognostic of subsequent lethality (6). 



Hemoconcentration 



In contrast to the above changes which are noticeable in the severely 

 irradiated animal, the concentrations of the cellular elements of the blood 

 are especially sensitive and their rate of formation rapidly reflects ac- 

 cumulated irradiation. Changes in the level of red and white cells have 

 long been associated with radiation effects. The production process of 

 either of these cell types is very sensitive to irradiation. However, im- 

 mediate response to radiation is usually noted in the concentration of 

 the white blood cells rather than the red for the reason that the duration 

 of life of the circulating erythrocyte is many days, whereas that of the 

 white cell is a few minutes (7). Hence, the concentration of white cells 

 will reflect early changes in their production. In Fig. 2 there is plotted 

 on a relative scale the concentration of white cells and lymphocytes as 

 a function of accumulated radiation. The values are for chronic expos- 

 ure rates of 0.1-15 r per day, and the data for mice, guinea pigs, and 

 rabbits are calculated from results given by Jacobson and Marks (8). 

 A slope of best fit has been drawn for both the total white-cell and the 

 lymphocyte count. The slope of the line indicates a 0.25 per cent change 

 in the white-cell or lymphocyte count per roentgen in these animals. In 

 the same figure there are plotted a number of therapeutic responses of 

 leukemic-cell concentration as a function of accumulated radiation from 

 radioactive phosphorus. The assumptions in this calculation are that 

 radioactive phosphorus has a combined biological and radioactive half 

 life of 7 days, and that the average concentration of the radioactive 

 phosphorus in the leukemic tissues is twice the average concentration 

 by the soft tissues. The least response to radiation by the leukemias 



