I t is a well known fact that organisms can stand a higher teniperature if the latter is raised gradually than if it is raised suddenly. This phenomenon is referred to in biology as a case of adaptation. Dallinger states that he succeeded in adapting certain protozoa to a temperature of 70" by gradually raising their temperature during several years.
Sehottelius had found that colonies of Micrococcus prodigiosus when transferred from a temperature of 22" to that of 38" no longer formed pigment and trimethylamin. When transferred back to the temperature of 18" to 22" the formation of pigment and of trimethylamin was resumed. After the cocci had been cultivated for ten or fifteen generations at 38" they failed to form pignient even when transferred back to 22". These experiments became the starting point for similar experiments by DieudonnB. He used Bacillus fluorescens putidus which forms a fluorescein pigment and trimethylamin. The optimal temperature for this bacillus is 22". At 35" it grew but did not form pigment or trimethylamin. Bt 3 7 O . 5 growth ceased. Reti urrsferred io 22^ pigment and trimethyiamin were again formed.
Dieudonn6l exposed a culture of this bacillus to 35". After twenty-four hours a second culture was taken from this and also kept at 35", and this process was repeated each day. The fifteenth generation thus cultivated at 35" began to form some pignient and from the eighteenth generation on, at 36" the formation