1919 Child; on Susceptibility of Algae 257 



come out again to any appreciable extent until the cell is killed, by accumula- 

 tion of the dye, by environmental conditions, or by the action of some other 

 agent following neutral red. In all forms except the Cladophora mentioned 

 above the death gradient in neutral red is much more strongly marked than 

 the staining gradient, and in forms with elongated cells, e. g., Callithamnion 

 is very distinct within the length of a single cell, although a staining 

 gradient is rarely distinguishable within the cell. Death in neutral red, as 

 indicated by the coagulation of the protoplasm into irregular masses which 

 at first become black or purple and then gradually lose their color as the 

 dye turns yellow, begins at the apical end of such a cell and may take 

 fifteen to thirty minutes to traverse the length of the eell and several hours, 

 in some cases a day or two, to pass over a few centimeters of axis, while the 

 staining gradient is slight and visible for only the first few moments of 

 staining. 



Since neutral red may attain a much higher concentration inside the 

 cell than outside and since it is not given up until death occurs, it is evident 

 that it must be adsorbed or held in some other way within the cell, and that 

 the ability of the cell to hold it is in some way associated with the living 

 condition. However the neutral red is held within the cell, it evidently 

 interferes with the physiological activities, since it becomes toxic and kills 

 in sufficient concentration. 



The relation of methylene blue to at least some algal cells differs in 

 certain respects from that of neutral red. Bonnemaisonia, for example, in 

 a 1/10000 solution of methylene blue takes up the dye readily and shows 

 at first a beautiful basipetal staining gradient as in neutral red. In 10 — 15 

 minutes the whole plant is stained deep blue, but on return to water the 

 dye begins to come out at once ; also with a basipetal gradient, the apical 

 ends of the axes becoming completely decolorized, while lower levels are still 

 deeply blue. In II/2 hours the whole is completely decolorized and appar- 

 ently quite uninjured, and the process of staining and decoloration may be 

 repeated many times. After staining one hour in 1/10000 methylene blue 

 complete decoloration requires 6 — 8 hours. Evidently the stain passes out 

 less readily than in. In Callithamnion much the same relations appear, a 

 distinct staining gradient and complete decoloration in water with a similar 

 gradient. Here, however, decoloration is almost as rapid as staining. For 

 these two forms methylene blue is apparently not toxic with the concentra- 

 tion and times of staining used, because, although it readily enters the cells, 

 it is not held to any marked degree and so is readily given up again when 

 the concentration gradient between inside and outside becomes sufficiently 

 steep. That it is held within the cell to some extent is indicated, first, 

 by the fact that its concentration within the cell may become much greater 

 than that outside, and second by its less rapid passage outward than inward. 



