In previous publications1we have shown, (1) that a small amount of acid added to an isotonic sodium chloride solution exerts a certain preserving effect on the amebocytes in a drop of Limulusblood surrounded by an excess of the solution. (2) That in tissue cultures of amebocyte tissue there occurs not only an active migration of the amebocytes into a sodium chloride solution, which has been made slightly acid, but that under certain conditions the addition of acid may increase the duration and intensity of this migration, which is followed by, or associated with, a formation of tissue-like structures not unlike those produced by the mesenchyme of vertebrates.2(3) That this effect of acid is due to its action on the cells, which consists in an increase in contraction and consistency of the protoplasm. (4) Inasmuch as we had previously shown that there exists a parallelism between the effect of various agencies on the state of contraction and consistency of the amebocytes on the one hand, and on the other hand, on the character of ameboid movement, the shape of pseudopods, the mode of movement of the granuloplasm, the power of resistance to the stereotropic tendency on the part of these cells, we found in accordance with these observations under the influence of acid a sharpening and lengthening of the pseudopods and a tightening of the granuloplasm and a greater state of contraction of the cells. (5) We found that it is possible, through grading the amount of acid added, to grade correspondingly the effects of the acid on the consistency of the cells in such a way that all gradations could be obtained from the extreme condition of round contracted cells, too hard to carry out ameboid movements, and contracted cells sending out very long, often multiple thread pseuclopodia, to a medium state in which the plasticity of the cell is greater and the ordinary tongue pseudopods are formed, and finally to the other extreme condition of cells which are very soft, which spread out readily and soon degenerate (Loeb & Blanchard).