20 AMCEBA LESS. 



From this it seems that an Amoeba, unless suffering a 

 violent death, is practically immortal, since it divides into 

 two completely organized individuals, each of which begins 

 life with half of the entire body of its parent, there being 

 therefore nothing left of the latter to die. It would appear, 

 however, judging from the analogy of the Infusoria (see 

 Lesson X.) that such organisms as Amoeba cannot go on 

 multiplying indefinitely by simple fission, and that occasion- 

 ally two individuals come into contact and undergo complete 

 fusion. A conjugation of this kind has been observed in 

 Amoeba, but has been more thoroughly studied in other 

 forms (see Lessons III. and X.). Whether it is a necessary 

 condition of continued existence in our animalcule or not, 

 it appears certain that "death has no place as a natural" 

 recurrent phenomenon " in that organism. 



If an Amoeba does happen to be killed and to escape 

 being eaten it will undergo gradual decomposition, becoming 

 converted into various simple substances of which carbon 

 dioxide, water, and ammonia are the chief. (See p. 90.) 



In conclusion, a few facts may be mentioned as to the 

 conditions of life of Amoeba the circumstances under 

 which it will live or die, flourish or otherwise. 



In the first place, it will live only within certain limits of 

 temperature. In moderately warm weather the temperature 

 to which it is exposed may be taken as about 15 C. If 

 gradually warmed beyond this point the movements at first 

 show an increased activity, then become more and more 

 sluggish, and at about 30 35 C. cease altogether, re- 

 commencing, however, when the temperature is lowered. 

 If the heating is continued up to about 40 C. the animalcule 

 is killed by the coagulation of its protoplasm (see p. 5) : it 

 is then said to suffer heat-rigor or death-stiffening pro- 



