310 HAOIATION niOLOGY 



clirt'ciciices ill the genos for tlioir maiiitciiaiico. In tlio protozoa, iiih(!ril- 

 ancc ill iiii<'a}2;(>s of cells niultiplyiiif? vegctatixciy ;is \v(»ll as iiihcrit.ancc 

 over the sexual processes can l)e investigated. Thus, in addition to the 

 classical mutation approach, (jther lines of investifi;ation may prove fruit- 

 ful. Actually, the inxestigations availal)le for this review ha\'(> added 

 only scattered bits of information along these lines. 



To the reviewer's knowledge, MacDougall (1929, 1931) was the first to 

 report the induction by radiation of inherited changes in protozoa. She 

 exposed mass cultures of the ciliate Chilodonella uncinatus to ultraviolet 

 from a (luartz merciiiv aic for brief periods on several successive days. 

 In some cultures abnormal animals appeared. A few of the abnormalities 

 proved to be inherited for many generations of asexual reproduction, and 

 in some cases through conjugation. These included apj)arent tetraploid 

 and triploid forms as well as others exhil)iting only changes in form and 

 size. Since the mutant forms appeared in only a few of the irradiated 

 cultures, the conclusion that they were induced by the radiation can 

 hardly l)e considered established, especially since the number of control 

 cultures is not given, but the aim of this woik was to obtain mutant forms, 

 not to investigate their origin. 



Alottram (1941, 1942) exposed cultures of an amicronucleate Col- 

 pidinm (said in a footnote to belong to this genus though called Para- 

 mecium in most of the text) to daily doses of ultraviolet or y radiation 

 (also to low and high temperatvn-es and to carcinogenic hydrocarbons). 

 After 4 to 62 days, a few abnormal animals were found. The doses of 

 ultraviolet are not given. The doses of y rays ranged from 800 to 

 12,1()0 r. The abnormals continued to produce abnormal descendants 

 though not necessarily of the same type. Somewhat similar changes 

 were produced by ultraviolet irradiation of Glaucoma sctosa. Investiga- 

 tions with Paramecium caudatum and Aspidisca sp. are also reported, but 

 it is not stated that radiation was employed. 



Mottram (1942) suggests that changes in viscosity are invoUed, that 

 the changes are cytoplasmic, not nuclear, and that they are similar to 

 those involved in carcinogenesis in higher forms. The arguments Mot- 

 tram gives for cytoplasmic and not nuclear change are inconclusive. 

 Nonetheless, it is hard to see how chromosomal changes could be involved 

 in an amicronucleate Colpidium. However, further investigation is 

 recjuired of both the origin and inheritance of these changes. It is espe- 

 cially necessary that the experiments permit a quantitative study of the 

 origin of the abnormalities followed by a careful genetic analysis of the 

 inheritance. 



Spencer and Calnan (1945), working with P. multimicronucleatum, 

 report a long-term deleterious effect of continuous sublethal exposures to 

 radium, to a number of dyes, and to methylcholanthrene. The animals 

 were grown in mass culture with continuous exposure to the agent. 



