648 BIOLOGICAL EFFECTS OF RADIATION 



(owing to the replacement of calcium by sodium ion), but there is no 

 further increase upon radiation. Apparently, therefore, the observed 

 gelation is dependent on the presence of the free calcium ion. 



Whereas the interior protoplasm or plasmasol is gelled by ultra-violet, 

 the outer cortex becomes more fluid. As far as can be judged from 

 centrifuge tests (which in the case of an outer ring of material of variable 

 width are not very accurate) the viscosity of the plasmagel decreases to 

 about one-fourth of its original value. This liquefaction of the plasmagel 

 is a characteristic effect produced by all sorts of stimulating agents. The 

 same effect can be produced by the withdrawal of the calcium ion. 



Heilbrunn and Daugherty therefore propose the theory that the 

 primary effect of irradiation is the release of bound calcium from the cell 

 cortex. The free calcium ion then enters the protoplasm proper, causing 

 first liquefaction and then gelation. Such indeed is the known action 

 of calcium ion on protoplasm, for a small addition of calcium ion produces 

 hquefaction, whereas larger amounts of free calcium cause a peculiar 

 coagulative reaction (136). 



The theory of Heilbrunn and Daugherty is supported by the fact 

 that irradiation actually does cause a release of calcium both from 

 living cells and from proteins. Thus Nadson and Rochline-Gleichgewicht 

 (269) report the formation of calcium oxalate in irradiated plant cells, 

 and Clark (63) claims that ultra-violet releases calcium from combination 

 with the proteins of the blood. Finally the recent work of Anslow and 

 Foster (7) and of Anslow, Foster, and Klingler (8) shows clearly how 

 ultra-violet radiation would act on the amino acid constituents of pro- 

 teins so as to release bound cation from combination. These authors 

 find that the rays break the carboxyl bond of the amino acid. 



The relation of calcium ion to the colloidal chemistry of protoplasm 

 is extremely interesting. This ion apparently bears the same relation 

 to the protoplasmic colloid that it does to the blood. The coagulation 

 of protoplasm is remarkably similar to the clotting of blood (136), and 

 it is only reasonable to assume that this would be true, for cells in general 

 are now known to contain all the materials involved in blood clotting 

 (100, 200, 201). 



When a cell is torn, the exuding protoplasm forms a film about itself. 

 Thus it clots just as blood does when it pours from a vessel. The 

 reaction involved is termed the surface precipitation reaction and takes 

 place only in the presence of free calcium. When a cell like a sea-urchin 

 egg is torn or broken, not only does a film form at the edge of the emerging 

 droplet, but numerous other films form within the droplet. Thus 

 vacuoles are produced, and these vacuoles may occupy a part or all of the 

 exuded drop or they may fill the entire cell. But neither the membrane 

 at the surface of the emerging drop nor the vacuoles can appear in the 

 absence of calcium. Hence calcium is involved in a soecies of reaction 



