180 PROTOZOOLOGY 



mental influences such as temperature and chemicals, and found that 

 the animals develop tolerance which is inherited through many gen- 

 erations even after removal to the original environment. For exam- 

 ple, one of the clones which tolerated only 1.1% of standard solution 

 of arsenic acid, was cultivated in gradually increasing concentrations 

 for four months, at the end of which the tolerance for this chemical 

 was raised to 5%. After being removed to water without arsenic 

 acid, the tolerance changed as follows: 22 days, 5%; 46 days, 4.5%; 

 151 days, 4%; 166 days, 3%; 183 days, 2.5%; 198 days, 1.25% and 

 255 days, 1%. As the organisms reproduced about once a day, the 

 acquired increased tolerance to arsenic was inherited for about 250 

 generations. 



There are also known inherited changes in form and structure 

 which are produced under the influence of certain environmental 

 conditions. Jollos designated these changes long-lasting modifica- 

 tions (Dauermodifikationen) and maintained that a change in en- 

 vironmental conditions, if applied gradually, brings about a change, 

 not in the nucleus, but in the cytoplasm, of the organism which 

 when transferred to the original environment, is inherited for a 

 number of generations. These modifications are lost usually during 

 sexual processes at which time the whole organism is reorganized. 



The long-lasting morphological and physiological modifications 

 induced by chemical substances have long been known in parasitic 

 Protozoa. Werbitzki (1910) discovered that Trypanosoma hrucei 

 loses its blepharoplast when inoculated into mice which have 

 been treated with pyronin, acridin, oxazin and allied dyes. Laveran 

 and Roudsky (1911) found that these dyes have a special affinity for, 

 and bring about the destruction by auto-oxidation of, the blepharo- 

 plast. Such trypanosomes lacking blepharoplast behave normally 

 and remain in that condition during many passages through mice. 

 When subjected to small doses of certain drugs repeatedly, species 

 of Trypanosoma often develop into drug-fast or drug-resistant 

 strains which resist doses of the drug greater than those used for the 

 treatment of the disease for which they are responsible. These modi- 

 fications may also persist for several hundred passages through host 

 animals and invertebrate vectors, but are eventually lost. 



Long-lasting modifications have also been produced by several 

 investigators by subjecting Protozoa to various environmental in- 

 fluences during the nuclear reorganization at the time of fission, 

 conjugation, or autogamy. In Stentor (Popoff) and Glaucoma 

 (Chatton), long-lasting modifications appeared during asexual divi- 

 sions. Calkins (1924) observed a double-type Uroleptus mohilis 



