INHERITANCE 717 



following way. Individuals from the depressed later generations are 

 cultivated side by side, under the same conditions, with individuals from 

 the same clone that have not lived under unfavorable conditions. One 

 of the two sets — the latter — multiplies rapidly and at a high level of 

 vitality. But the former set, that has lived under unfavorable conditions, 

 multiplies slowly, at a low level of vitality, in a degenerate condition. 



Thus in these Protozoa we find realized what some have held must 

 occur in mankind: the production of inherited degeneration, by long- 

 continued bad living conditions. 



Discussion of the nature of these changes will be reserved until other 

 inherited environmental modifications have been considered. 



INHERITED ACCLIMATIZATION AND IMMUNITY 



The changes in inherited characters induced by unfavorable environ- 

 mental conditions are not always degenerative in character. In the uni- 

 cellular organisms, as in multicellular organisms, long exposure to un- 

 favorable conditions may result in the production of acclimatization or 

 immunity. In the Protozoa, after removal from the unfavorable condi- 

 tions, 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 hundreds of vegetative 

 generations. 



But in the course of many generations under the favorable conditions, 

 with the injurious agent no longer present, the acquired immunity 

 becomes gradually less marked; it slowly decreases, and, finally, in a 

 sufficiently long period it is lost. But this may not occur until months 

 after removal from the immunizing agent, during which time the 

 acquired immunity is inherited. 



Such acquisition of inherited immunity is most extensively known in 

 parasitic Protozoa and in pathogenic bacteria, since in these organisms 

 it is of medical importance. Detailed accounts of the knowledge in these 

 fields will be found in the treatise of Taliaferro (1929). 



But acquisition and inheritance of acclimatization or immunity occurs 

 also in free-living Protozoa. A somewhat detailed review and discussion 

 of investigations in this field will be found in the author's Genetics of 

 the Protozoa (1929). Here only brief summaries of some of the more 

 important investigations in this field can be presented. 



