5. Dallinger stated that he succeeded in adapting certain protozoans to a temperature of 70° C. by gradually raising their temperature during several years. It is desirable that this statement be verified; until this is done doubts are justified. Schottelius found that colonies of _Micrococcus prodigiosus_ when transferred from a temperature of 22° to that of 38° no longer formed pigment and trimethylamine. After the cocci had been cultivated for ten or fifteen generations at 38° they failed to form pigment even when transferred back to 22° C. Dieudonné[283] used _Bacillus fluorescens_ for similar purposes. At 22° it forms a fluorescing pigment and trimethylamine, but not at 35°. By constantly cultivating this bacillus at 35° Dieudonné found that after the fifteenth generation had been cultivated at 35° the bacillus produced pigment and trimethylamine at 35°. Davenport and Castle[284] found that tadpoles of a frog kept at 15° went into heat rigour at 40.3° C., while those kept for twenty-eight days at 25° were not affected by this temperature but went into heat rigour at 43.5°. When the latter tadpoles were put back for seventeen days to a temperature of 15° they had lost their resistance to high temperature partially, but not completely, since they went into heat rigour at 41.6°. The authors suggest that this adaptation to a higher temperature is due to a loss of water on the part of protoplasm, whereby the latter becomes more resistant to an increase in temperature. This idea was put to a test by Kryž[285], who found that the coagulation temperature of their muscle plasm is not altered by keeping cold-blooded animals at different temperatures. [283] Dieudonné, A., _Arb. a. d. kais. Gesndhtsmt._, 1894, ix., 492. [284] Davenport, C. B., and Castle, W. E., _Arch. f. Entwcklngsmech._, 1896, ii., 227. [285] Kryž, F., _Arch. f. Entwcklngsmech._, 1907, xxiii., 560. Loeb and Wasteneys[286] found that _Fundulus_ taken from a low temperature of 10° C. die in less than two hours when suddenly transferred to sea water of 29° C.; and in a few minutes if suddenly transferred to a temperature of 35° C. If, however, the fish were transferred to a temperature of 27° C. for forty hours they could live indefinitely in sea water of 35°. By exposing the fish each day two hours to a gradually rising temperature they could render them resistant to a temperature of 39°. The remarkable fact was that fish if once made resistant to a high temperature (35°) did not lose this resistance when kept for four weeks at from 10° to 14° C. Control fish taken from the same temperature died in from two to four minutes; immunized fish taken from 10° and put directly to 35° C. lived for many hours or indefinitely. They will even retain this immunity when kept for two weeks at a temperature of 0.4° C. [286] Loeb, J., and Wasteneys, H., _Jour. Exper. Zoöl._, 1912, xii., 543.