VI. SELECTION AND ISOLATION 395 



Strain retained its resistance during hundreds of vegetative divisions 

 in an arsenic-free medium before beginning to revert gradually to its 

 former sensitivity. However, if conjugation of two resistant cells 

 occurred, the progeny became completely sensitive. It should be noted 

 that irregular fluctuations of temperature and other changing condi- 

 tions hastened the de-adaptation, though not so conspicuous as conju- 

 gation. As was already emphasized, the rejuvenation or the recovery 

 of- the former structure is caused generally by the disturbance of the 

 structure ; the effect of the conjugation or the fertilization is based 

 upon this disturbing action. 



A similar phenomenon is also kown with trypanosomes, rendered 

 resistant against arsenophenylglycine. The resistance can be retained 

 for considerably long periods, but a passage through a rat louse and 

 then to a healthy rat the resistance is lost completely, thereby the 

 trypanosomes become highly susceptible to the drug (73). As was 

 previously discussed, in the respect of the rejuvenescence the host 

 change is analogous to the fertilization. 



However, inspite of such rejuvenating action of fertilization, 

 whereby the recovery of the original pattern will be facilitated, there 

 are numerous evidences showing that acquired characters even of 

 higher organisms are transmissible to progeny, though of a transient 

 nature. The wheat of a south country can shorten the period required 

 for reaching the maturity, when removed to the north and cultivated 

 there for prolonged periods. Such an acquired character is likely to 

 be retained for several generations even wheh the wheat is removed 

 to the south. It is well acknowledged that various characters, based 

 upon habitats, of cultivated plants tend to continue even when the 

 plants are transplanted to entirely different places, although the char- 

 acteristics will diminish gradually. The same has been reported 

 with water-flea having the shape varying with the habitats. 



It has been confirmed that the acquired character to produce 

 antibodies to some antigens can sometimes be transmitted to progeny. 

 Thus, domestic doves and chickens immunized with some viruses 

 transmit the character to produce the virus-neutralizing antibody 

 through the egg to their offspring, although immunity conferred on 

 the offspring is short, lasting a maximum of 12 weeks in doves and 

 of 4 weeks in chickens (73a). This may be regarded as the transmis- 

 sion to the progeny of the antigenic pattern impressed in the anti- 

 body-producing cells by the virus. 



The transmission of the very pattern of bacteria or of the viruses 

 to the offspring through germ cells of the host, a phenomenon which 

 was repeatedly discussed, should be likewise regarded as a kind of 

 a durable modification. The pattern is to be lost sooner or later even 



