568 BIOLOGY OF THE PROTOZOA 



zation was unchanged although the new (l()ii})le type of organism 

 lived for four hundred and five days and divided 307 times. 



Variations due to environmental changes should be retained as 

 long as such changes are maintained. Thus Zuelzer obtained a 

 very different type of organism })y transferring Ainoeha verrucosa 

 from fresh to salt water. The variation lasted as long as the 

 organisms were kept in salt water but reverted to the original 

 form on transference to fresh water again. Jennings (1921) cites 

 a number of cases of bacteria in which the organization appeared 

 to be permanently changed l)y a temporary change of drastic char- 

 acter in the mediiun. Similar results have been obtained M'ith 

 Protozoa where adaptations or responses of the organism to solutions 

 of gradually increasing concentrations or to slowly increasing tem- 

 perature changes have apparently liecome permanent, or at least 

 endure for many generations by division. Among the first, and the 

 more extensive of such experiments, were those of Dallinger and 

 Drysdale (1873) in connection with the life histories of different 

 flagellates. Dallinger (1907) in particular, working with remark- 

 al)le patience and perseverence for seven years was able to accustom 

 three species of flagellates which are described as Tetramitus ros- 

 tratvs, Monas daUingeri, and Dallingeria drysdali to temperatures 

 which are fatal to these organisms under normal conditions of 60° F. 

 At the beginning of the experiment all individuals were killed by 

 a sudden change to 78° F., but b\' accustoming them to slowly 

 increasing temperatures acting for long periods they became 

 adapted to this condition. Such adapted individuals w^ere then 

 subjected to further increases in temperature, the change from 

 one degree of heat to another often requiring months of patient 

 waiting. Finally he obtained individuals which continued to live 

 vigorously in a temperature of 158° F. Here was a change in 

 organization or an adaptation to changed conditions which persisted 

 as long as the conditions were maintained and until an accident 

 brought the experiment to an end. 



Similar but less extensive experiments have been carried on with 

 other Protozoa. Within the last decade Middleton (1918) and 

 Jollos (1913, 1923) have tested the effect of increased temperatures 

 on ciliates. Middleton (1918) separated progeny of an individual 

 of Styhnychia imstuJaia into two groups one of which was kept for 

 some thirty days at a relatively high temperature (about 30° C.) 

 the other at a low temperature (10° C). The set at 30° C. divided 

 more rapidly than those at 10° C. They were then transferred to 

 a common intermediate temperature in which the previously 

 warmed individuals continued to divide more acti^'el^' than the 

 cooled set. Evidence of the same type is furnished by the iliteresting 

 experiments of Hartmann (1924) on Evdorina cJegans and Gonium 

 pectorale. By use of potassium nitrate and ammonium chloride 



