IRRADIATION OF LIVING PROTOPLASM 651 



types of external agents and to respond to many diverse treatments in 

 much the same manner. 



In general, most authors are agreed that roentgen rays and radium 

 radiation cause first a decrease in viscosity and then, on longer exposure, 

 a sharp increase in viscosity or coagulation. As early as 1897, Lopriore 

 found that roentgen rays caused an increase in the rate of protoplasmic 

 streaming in leaf cells of Vallisneria spiralis. This was when the leaves 

 were exposed for half an hour. After an hour's exposure, streaming 

 stopped and the protoplasm became yellow, granular, and coarsely 

 vacuolar. Seckt (340) found similar effects of roentgen rays on proto- 

 plasmic streaming in various plant cells, and the same type of phenomenon 

 has also been described for two species of Amoeba (Schaudinn, 328). 



Using radium, Zuelzer and Philipp (401), and more recently Petchenko 

 (286), also described changes in the rate of amoeboid movement. The 

 former authors used gamma and hard beta rays from preparations con- 

 taining 40, 26, 15, and 13 mg. of radium, upon Amoeba diploidea, the 

 latter studied Amoeba vahlkamyfia with 5 and 10 mg. RaBr2. These 

 studies agree ; there is first a pronounced acceleration of the rate of stream- 

 ing, indicating, according to Zuelzer and Philipp, a decreased viscosity. 

 With prolonged irradiation, movement becomes much slower than the 

 normal, the amoebae round up and become full of small vacuoles. These 

 experiments indicate an initial decrease in viscosity followed by a sharp 

 increase, but it must be remembered that the rate of protoplasmic 

 streaming or of amoeboid movement is an uncertain index of protoplasmic 

 viscosity. For the speed of movement depends not only on the viscosity 

 but also on the unknown forces which pTropel the protoplasm. 



In relatively recent years, more certain methods of viscosity deter- 

 mination have been used. Weber (386) radiated Spirogyra cells with 

 170 Holzknecht units but found no effect on viscosity when tested by the 

 centrifuge method. After 20 hr., it is true, there was a viscosity increase, 

 but this W^eber interpreted as a secondary effect. Weber also radiated 

 Phaseolus seedlings with 24 Holzknecht units, but he could detect no 

 viscosity change. Doubtless the dosage used by Weber was too low for 

 the types of protoplasm he studied. 



Williams (1923) was able to find a very definite effect on the proto- 

 plasm of the stalk cells of Saxifraga umbrosa. Short exposures to either 

 roentgen rays or to radium beta or gamma rays caused an increase in the 

 rate of protoplasmic streaming and also an increase in the rate of Brown- 

 ian movement of small particles in the protoplasm. Longer exposures 

 caused slowing and stoppage of streaming. Following such long expo- 

 sures there was extensive vacuolization. 



Nakashima (272) irradiated isolated cells from the salivary glands 

 of the snail Limnaea (40 kv., 10 ma., 6 hr., 30 cm.) and observed an 

 acceleration of Brownian movement in the protoplasmic granules. But 



