PROTOPLASM AND ITS PROPERTIES. 



129 



(1) Absorption. 



(2) Metabolism. 



(3) Excretion. 



(4) Reproduction and growth. 



(5) Automatic powers.-' 



(6) Contraetilit}-. 



(7) Irritabilitj-. 



(1), (2), and (3) are not so readily studied in 

 the slime-moulds as in some other plants, but 

 unless one can believe in the manufacture of 

 something out of nothing, he must conclude 

 that these simple plants make their growth 

 at the expense of materials drawn from the 

 water and the decaying matter on which they 

 are found.^ 



Another important characteristic of living 

 protoplasm, which the student may establish 

 by his own experiments, is : the power of 

 resisting some chemical and physical chauges. 



Living cells and their contents are not always 

 affected by acids, alkalies, staining solutions, 

 heat or cold as the same material would be 

 affected after it is dead or before it becomes 

 alive. 



163. Circulation of Protoplasm. — When 

 confined by a cell wall, protoplasm often mani- 

 fests a beautiful and constant rotating move- 

 ment, traveling incessantly up one side of the 



^ 



Fig. 103.— Sting- 

 ing Hair of Net- 

 tle, with Nucleus. 



The arrows show 

 the direction of 

 the currents "in 

 the protoplasm. 



' That is, the power of originating movements not whoUy and directly caused by 

 any external impulse, for instance, the lashing motion of the cilia of the swarm- 

 spores of slime-moulds or the slow periodic movements of some leaves, even when 

 exposed to an unchanging temperature and amount of light. 



2 It would of course be well for the pupil to make careful studies of Amcsba and 

 of one or more of the ciliated animalcules. If time will admit of this, the teacher 

 may consult Huxley and Martin's Elementary Biology, under Amceba and Vorticella. 



