CHROMOSOMES AND CYTOPLASM IN PROTOZOA 



49 



acquired immunity has been inherited for 

 many vegetative generations. 



Such acquirement of inherited immunity 

 is most extensively known in parasitic 

 Protozoa and in pathogenic bacteria, be- 

 cause in these it is of practical importance. 

 But it occurs, also, according to the investi- 

 gation of Jollos, Neuschloss, Dallinger, and 

 others, in free-living Protozoa. Such free- 

 living Protozoa have been acclimatized to 

 injurious intensities of temperature, and of 

 solutions of arsenic, antimony, quinine, 

 methyline blue, and various organic chem- 

 icals. In these matters we are obviously 

 dealing with adaptive changes, as com- 

 pared with the degenerative changes which 

 were discussed first. 



The third category of inherited changes 

 produced by environmental conditions con- 

 sists of alterations of form and structure 

 which are not clearly matters either of 

 degeneracy or of adaptation. In some 

 Protozoa individuals that have lived for 

 many generations under special conditions 

 have peculiarities of form and structure. 

 When they are removed from these special 

 conditions they retain for many genera- 

 tions — often for hundreds of generations — 

 these peculiarities of form and structure. 

 But gradually in the course of long periods 

 under the new conditions, they lose the 

 special peculiarities resulting from the 

 former conditions, and take on character- 

 istics such as are shown by those stocks 

 that have always lived under the later 

 conditions. Many remarkable instances of 

 such inherited environmental effects have 

 been described in flagellates recently by 

 Moewus (1934). 



In attempting to interpret these in- 

 herited environmental modifications, and 

 particularly in trying to discover their seat 

 in the cell, much significance has been at- 

 tached to certain peculiarities which some 

 or all of them show. First, as before men- 

 tioned, after a great number of genera- 

 tions have passed under conditions that 

 are free from the agents that produced 

 them, the acquired modifications gradually 

 fade away. This is known to be true for 

 acquired immunity and for structural 



modifications induced by special conditions. 

 It is not known to be true for degenerative 

 changes induced by unfavorable conditions. 



Second, the inherited environmental 

 modifications very commonly disappear 

 when sexual reproduction occurs. The 

 descendants of individuals that have con- 

 jugated may not show the depression and 

 degeneration seen in their ancestors. They 

 often lose at the occurrence of conjugation 

 the immunity or acclimatization that has 

 been acquired and inherited by their for- 

 bears. It is a peculiar and striking fact, 

 however, that conjugation does not always 

 bring about these results. After conjuga- 

 tion many of the depressed individuals 

 show a renewal of vitality, an increase in 

 rate of multiplication. But some of the 

 descendants from the conjugated individu- 

 als do not. Some are left still depressed 

 in vitality, or are indeed in a worse condi- 

 tion after conjugation than before. The 

 renewal of vitality in depressed stocks 

 through conjugation is famous under the 

 name of rejuvenescense. 



A similar situation exists with relation 

 to inherited acclimatization or immunity. 

 It commonly disappears at conjugation; 

 the descendants of the individuals that 

 have conjugated no longer show the greater 

 resistance to injurious conditions. But, as 

 in the case of inherited degeneration, in 

 some cases this does not occur. In some 

 cases the descendants of the individuals 

 that have conjugated continue to manifest 

 the acquired immunity. 



These two peculiarities — the gradual dis- 

 appearance of the inherited modifications 

 when removed from the agents that induced 

 them, and their frequent disappearance 

 after conjugation has occurred — have led 

 certain investigators to place them in a 

 different category from inherited charac- 

 ters determined by peculiarities of the 

 chromosomal materials. Jollos, who has 

 worked and theorized much on these mat- 

 ters, led by these considerations, has 

 assigned these inherited modifications to 

 the cytoplasm instead of to the nuclear 

 constituents. A change in the genes, a 

 mutation, he urges, is a permanent change ; 



