Davenport and Castle carried out a series of experiments on the egg of the toad, in which they tried to acclimatize the eggs to a temperature higher than normal. Recently laid eggs were used; one lot kept at a temperature of 15 degrees C., the other at 24-25 degrees C. Both lots developed normally. At the end of four weeks the temperature point at which the tadpoles were killed was determined. Those reared at a temperature of 15 degrees C. died at 41 degrees C., or below; those reared at 24-25 degrees C. sustained a temperature 10 degrees higher; no tadpole dying in this set under 43 degrees C. “This increased capacity for resistance was not produced by the dying off of the less resistant individuals, for no death occurred in these experiments during the gradual elevation of the temperatures in the cultures.” The increased resistance was due, therefore, to a change in the protoplasm of the individuals. It was also determined that the acquired resistance was only very gradually lost (after seventeen days’ sojourn in cooler water). The explanation of this result may be due, in part, to the protoplasm containing less water at higher temperatures, for it is known that while the white of egg (albumen) coagulates at 56 degrees C. in aqueous solution; with only 18 per cent of water it coagulates between 80 degrees and 90 degrees C.; and with 6 per cent, at 145 degrees C.; and without water between 100 degrees and 170 degrees C. It has long been known that organisms in the dry condition resist a much higher temperature. The damp uredospore is killed at 58.5 degrees to 60 degrees C.; but dry spores withstand 128 degrees C. It is also known that organisms may become acclimatized to cold through loss of water, but we lack exact experimental data to show to what extent this can be carried. There are also some experiments that go to show that animals may become attuned to certain amounts of light, but the facts in this connection will be described in another chapter. Some important results have been obtained by accustoming organisms to solutions containing various amounts of salts. A number of cases of this sort are given by De Varigny. It has been found that littoral marine animals that live where the water may become diluted by the rain, or by rivers, survive better when put into fresh water than do animals living farther from the shore. Thus the oyster, the mussel, and the snail, Patella, withstand immersion in fresh water better than other animals that live farther out at sea. The reverse is also true; fresh-water forms, such as Lymnæa, Physa, Paludina, and others may be slowly acclimatized to water containing more salt. The forms mentioned above could be brought by degrees into water containing 4 per cent of salt, which would have killed the animals if they had been brought suddenly into it. Similar results have been obtained for amœba.