IRRADIATION OF LIVING PROTOPLASM 643 



exposed the cells to heat comparable to that of the roentgen apparatus, 

 and obtained the same acceleration of the sedimentation rate. 



EFFECTS ON PROTOPLASMIC COLLOIDS 



A living cell is more than a semipermeable membrane. Although 

 cell physiologists so often discuss the osmotic membranes of cells and 

 their changes in permeability, there can be no doubt that the interior 

 protoplasm is at least equally important. It is commonly held that all 

 types of stimulation cause an increased permeability of the plasma mem- 

 brane, but very few authors have tried to explain how such an increase 

 in permeability would affect the main mass of the protoplasm. Accord- 

 ing to some, electrical phenomena are involved, but the nature of such 

 postulated electrical disturbances and how they affect the protoplasmic 

 colloids are not at all clear. It might also be possible that with increased 

 permeability, the ions surrounding the cell exert some particular action. 

 No evidence for this latter view has been presented. 



But whether or not it is possible to relate permeability change to a 

 change in the interior, certain it is that the protoplasm itself is pro- 

 foundly affected by stimulation in general and by radiation in particular. 

 Radiologists have often sought to interpret protoplasmic effects in terms 

 of the known action of rays on inanimate proteins. The fallacy of this 

 type of argument has already been pointed out. It is certain, at least, 

 that the colloidal properties of protoplasm are vastly different from those 

 of any known protein, so that any attempt to interpret living substance 

 in terms of protein must be made cautiously. The colloidal study of 

 protoplasm is not easy. Microscopic observation alone is extremely 

 uncertain, for complete coagulation of the cell contents is not necessarily 

 accompanied by readily observable change. Not infrequently early 

 authors who merely examined the general appearance of the protoplasm 

 have mistaken liquefaction for coagulation and vice versa. 



Fortunately, within recent years it has become possible to make 

 reasonably accurate measurements of protoplasmic viscosity. These 

 give indications of colloidal change. In some respects, however, viscosity 

 studies of the living colloid are different from those of inanimate systems. 

 In a test tube, coagulation is accompanied by a settling out of a precipi- 

 tate. Within a tiny cell, no such settling out occurs. Either coagulation 

 or gelation is indicated by a pronounced increase in protoplasmic viscos- 

 ity. It is, however, not certain that the ordinary terminology of colloid 

 chemistry is altogether appropriate for the living colloid. Protoplasm 

 occurs in minute droplets; it is typically a suspension with 20 or 30 per 

 cent or even more of suspended granular material. One can scarcely 

 consider it in the same terms as a 1 per cent solution of egg albumen. 

 But one can say very definitely that large changes in viscosity occur in 

 the protoplasm, and that these are measurable. 



