344 BIOLOGY OF TEE PROTOZOA 



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 few years Middleton (1918) and 

 Jollos (1918, 1923) have tested the effect of increased temperatures 

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

 of Stylonychia pustulaia 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 actively than the 

 cooled set. 



Experiments of this type and others to be described below show 

 that changes in organization can undoubtedly be produced in 

 Protozoa. If such changes are permanent they may be interpreted 

 as mutations; if not permanent they have little more value than 

 the fluctuating variations which accompany changes of metabolism. 

 The great majority of changes which have been described are cer- 

 tainly not mutations but illustrate the flexibility of protozoan 

 organizations and broaden the limits within which fluctuating varia- 

 tions are known to occur. Such variations ultimately revert to type 

 and although they may last for many generations by division, they 

 have no permanent effect upon the organization. Jollos (1913) 

 terms them "enduring modifications" (I)auermodificationen). 

 Other frequently-cited illustrations of this type of variations have 

 to do with the effects of minute doses of poison on the organi- 

 zation. Some races of Trypanosoma for example, may become 

 adapted and immune to weak doses of arsenic— the so-called 

 poison-fast, arsenic-fast, atoxyl-fast races first described by Ehrlich. 

 Bignami (1910) thus interprets malaria relapses as due to quinine- 

 fast organisms. Such modified types retain their immunity for 

 long periods and through many successive generations of trans- 

 plants but they apparently belong to this type of enduring modifica- 

 tions. Gonder (1912) has shown that poison-fast races of Trypano- 

 soma lewisi lose their acquired immunity by passing through the 

 rat flea. Also races of Trypanosoma without parabasal bodies 

 (Blepharoplastlose) first obtained by Werbitzski (1910) by injecting 

 pyronin into the host's blood, would live for many generations of 

 transplants without this kinetic element, but the parabasal body 

 ultimately reappears. Here too in all probability should be included 



