48 



THE CELL. AND PROTOPLASM 



problem of differentiation in multicellular 

 development, it may tackle the puzzles of 

 differentiation, localization, and functional 

 organization in these enormously complex 

 single cells. [See an interesting attempt in 

 this direction in the case of the giant algal 

 cell of Acetabularia (Hammerling 1934).] 



But it is not problems of development, 

 but of genetics, that I wish to call to your 

 attention in these organisms. 



The "doctrine of the inheritance of ac- 

 quired characteristics" finds its last refuge 

 in the genetics of Protozoa. It is a fact 

 that Protozoa are modified in many ways 

 by the action of environmental conditions, 

 and it is known that the modified character- 

 istics so induced are inherited for long 

 periods in vegetative reproduction — for 

 hundreds of generations. By some investi- 

 gators, notably by Jollos and his followers, 

 it is maintained that these inherited envir- 

 onmental modifications affect the cytoplasm 

 only. From this, if correct, it follows that 

 diverse conditions of the cytoplasm are 

 transmitted to different offspring and that 

 these diverse cytoplasmic conditions pro- 

 duce diverse inherited characteristics in the 

 descendants. The cytoplasm, if this be 

 true, shares with the chromosomes the func- 

 tion of producing inherited differentiations 

 between individuals, so that it must be ac- 

 counted a part of the genetic material. 



To appreciate the genetic situation, a 

 brief review of some of the phenomena must 

 be presented. The heritable modifications 

 induced by environmental conditions in 

 Protozoa may be classified in three groups. 

 First, there are degenerative changes in- 

 duced by unfavorable conditions acting for 

 many generations. When eiliate infusoria 

 are bred for hundreds of vegetative genera- 

 tions under conditions to which they are 

 not entirely adapted, they gradually ''run 

 down"; their vital processes become de- 

 pressed, slow, inefficient. In time the ani- 

 mals become distinctly degenerate, abnor- 

 mal in form and structure, and reduced in 

 size. As an index of this decrease in vital- 

 ity the changes in the rate of multiplication 

 are useful. The frequency of cell division 

 becomes reduced, and this is accompanied 



by a lowering of vitality in all functions. 

 These changes are shown in the familiar 

 graphs which register the gradual slowing 

 up of the rate of multiplication. In the 

 later generations this rate is very low. Now 

 if individuals of these later generations are 

 cultivated under conditions identical with 

 those of the same stock which have not 

 lived for a long time under unfavorable 

 conditions, it is found that the depression 

 and degeneracy are inherited. Under the 

 same conditions, one of the two sets multi- 

 plies rapidly and at a high level of vitality ; 

 the other slowly and at a low level of vital- 

 ity, and in a degenerate condition. These 

 differences continue for generation after 

 generation, for a great number of genera- 

 tions. An immense amount of work with 

 these results has been carried on by many 

 investigators. In these Protozoa, therefore, 

 we find realized what some have held must 

 occur in mankind : the production of in- 

 herited degeneracy by long-continued bad 

 living conditions. 



The second type of inherited change in- 

 duced by environmental conditions is ac- 

 climatization, or the acquirement of im- 

 munity. The Protozoa share with higher 

 animals the power of developing immunity 

 to certain injurious agents — the power of 

 becoming acclimatized to high and low 

 temperatures or to injurious concentrations 

 of chemicals. To produce these results in 

 the Protozoa, they are subjected for many 

 generations to gradually increasing inten- 

 sities of the injurious agent. And after 

 removal from the injurious conditions the 

 acquired acclimatization or immunity is 

 inherited in vegetative reproduction for 

 many generations. Cases are on record in 

 which such inheritance continued for many 

 months, including some hundreds of gen- 

 erations. 



But in the course of these many gener- 

 ations under favorable conditions, that is, 

 with the injurious agent no longer present, 

 the acquired immunity gradually becomes 

 weaker and less marked ; it slowly decreases 

 and finally is lost. But this may not occur 

 till months have passed after removal from 

 the immunizing agent ; during this time the 



