1919 Child; an Susceptibility of Algae 251 



In the red algae the pigment (phj^coerythrin) is to some extent an 

 acid-alkali indicator. When the plants are killed in alkaline solution, the 

 color changes to yellow, while in acids the change is first to purple and 

 then usually to whitish, and in neutral agents a gradual loss of the red 

 or brownish red color occurs, the plant becoming successively light red, 

 pinkish and whitish or pinkish white. Evidently in acid and alkaline 

 solutions the pigment is first changed in color and then, at least in acids, 

 gradually diffuses out into the surrounding fluid, while in neutral agents 

 the diffusion from the cell occurs, but with little or no change in the color 

 of the pigment. 



In the forms wuth large cells it can readily be seen that the pigment 

 changes are accompanied by break-up and coagulation of the protoplasm. 

 The exact moment among these changes when death occurs cannot of 

 course be determined, but the course of these changes and the times at 

 which they occur in different parts of the plant or of single cells can be 

 determined, and these data show the differences in susceptibility. 



Methylene blue in the concentrations used (1/100000, 1/10000) is 

 apparently not toxic or only slightly toxic to some species of red algae, 

 although it enters the cells very readily and accumulates there, but some 

 interesting data on penetration were obtained with it. 



Potassium permanganate is reduced by protoplasm to MnOj which 

 stains the protoplasm brown. It has been noted elsewhere that with 

 this agent the physiological differences along the axis in animals appear 

 very distinctly as color gradients, the differences in color depending upon the 

 rate of reduction of the agent at different levels of the axes (Child, 1919a). 

 With certain concentrations gradients in disintegration of the protoplasm 

 also appear. This agent was used in concentrations from m/ 10000 — 

 m/1000 with a number of algae and gave beautiful color gradients, and in 

 certain forms with large, elongated cells, the disintegration gradients in 

 the single cells could also be clearly seen. 



The development of the susceptibility method is based upon the con- 

 clusion from various lines of evidence that susceptibility to certain agents, 

 such, for example, as the cyanides, which are powerful reducing agents 

 ajid inhibitors of oxidation in living protoplasm, shows a certain general 

 relation to the rate of oxidation in protoplasm. In the course of experi- 

 mental work with a large number of animal forms ranging from the pro- 

 tozoa to the vertebrates, evidence has been accumulated along many differ- 

 ent lines to show that susceptibility, not only to the cyanides but to at 

 least many other agents, including anesthetics, acids, alkalies, salts, and 

 "vital" dyes, and even to such conditions as extremes of temperature and 

 lack of oxygen when no chemical agent is used, conforms to the same 



