. Experimental morphology. Protoplasm; Growth. §2] ACCLIMATIZATION TO CHEMICAL AGENTS 31 The facts obtained by us clearly indicated, then, that, without selection, — for no deaths occurred in our culture solutions, — the protoplasm may become modified merely by subjection to the poison, so as to gain an increased resistance to it. Hence the acclimatizations that we find in nature need not have been brought about by natural selection — must have occurred, indeed, even without selection, if the organisms had been gradually subjected to their environment. go 8EC8.. Fig. 1. 40 SECS. STRENGTH OF CULTURE SOLUTIONS -Curve of resistance periods to a 0.00125% solution of HgCla of Stentors reared in various solutions of HgClg during 20 to 96 hours. We did not determine for how long a time the acclimatized Protozoa retained their heightened resistance capacity. The only data we have upon the subject of persistence of acclima- tization is derived from studies on Vertebrates. Thus it is the familiar experience of arsenic eaters that, after they have broken off their habit, the body does not quickly return to a normal condition. Even after a considerable period of self-denial the taking of large doses may be recommenced — must be recommenced, indeed, or illness sets in. Ehblich ('91) has studied experimentally the phenomenon. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Davenport, Charles Benedict, 1866-1944. New York, The Macmillan company; London, Macmillan & co. , ltd.