72 BIOLOGY OF DEATH 



life; by replacing at intervals the worn out material with this reserve, 

 the animals are kept in a state of perpetual vigor; not, as individuals, 

 growing old or dying a natural death. Nevertheless, a wearing out pro- 

 cess, such as might be called getting old, does occur in the structures 

 employed in the active functions of life, and these must be replaced after 

 a time of service. So far as the conditions in these organisms are typical, 

 deterioration and death do appear to be a consequence of full and active 

 life; life carries within itself the seeds of death. It is not mating with 

 another individual that avoids this end; but replacement of the worn 



material by a reserve The great mass of cells subject to death in the 



higher animals dwindles in the infusorian to the macronucleus ; this alone 

 represents a corpse. But the dissolution of this corpse occurs within 

 the living body. It much resembles such a process as the wasting away 

 and destruction of minute parts of our own bodies, which we know is 

 taking place at all times, and which does not interrupt the life of 

 the individual." 



It is doubtful if this position is -warraiited. Since 

 Jennings wrote the statement quoted, some; new and 

 pertinent data have appeared in regard to amicronu- 

 cleate infusoria. Woodruff and his co-workers have 

 shown that such races may occur rather commonly. Thus 

 Woodruff, in 1921, says: 



"During the past year, the isolation for certain experiments of 14 

 "wild" lines representing 6 species of hypotrichous ciliates revealed 7 lines 

 (4 species) with micronuclei and 7 lines (2 species) without morphological 

 micronuclei. Ten of the lines were all isolated from a "wild" mass culture 

 of the same species Urostyla grandis, found in a laboratory aquarium. 

 Six of these lines were amicronucleate. All of the lines of all of the 

 species have bred true with respect to the character in question, and one 

 amicronucleate line at present is at the 102d generation. 



Similarly a culture of Paramecium caudatum, which the present writer 

 supplied a year ago to a course in protozoBlogy for the study of the nucleus, 

 failed to reveal a micronucleus, although in other races the micronucleus 

 was readily demonstrated." 



Now, since it is the micronucleus which furnishes for 

 the process of endomixis the "reserve stock of a material 

 essential to life" which Jennings discusses, it is plain 

 that the existence of amicronucleate races of Protozoa 



