Ch. Ill, 5] 



PROTOPLASM 



39 



the vitalistic conception of organic nature held by some 

 biologists, and the latter with the mechanistic conception 

 held by others. 



Protoplasm is unique in possessing simultaneously two 

 sets of properties, physical and physiological. Its physical 

 properties, — color, den- 

 sity, weight, hardness, etc., 

 — are of course simply the 

 aggregate of the proper- 

 ties of its many con- 

 stituent substances. Its 

 physiological properties 

 are those which are pecul- 

 iar to itself as the living 

 material. They are mani- 

 fest most clearly in the 

 physiological processes of 

 plants which they make 

 possible; and we need 

 here but give, for the 

 sake of completeness, and 

 rather for future reference 

 than present learning, the 

 mere roll of their names, 

 viz. automatism, regula- 

 tion, metabolism, mobility, division, growth, irritability, 

 heredity, variability, morphological plasticity. 



All protoplasm originates, and therefore all organisms 

 arise, in only one way, so far as known, and that is by 

 growth and division (or reproduction) of preexisting proto- 

 plasm. Spontaneous generation, or the formation of 

 protoplasm anew out of non-living materials, is not known 

 to occur anywhere in nature ; for all supposed cases thereof 

 when investigated by scientific methods have been found 

 to be only apparent and not real, as Pasteur was the first to 

 prove. Thus we can trace back all existent living beings 



Fiq. 14. — Portion of the body (Plas- 

 modium) of a Slime-mold ; X 225. Such 

 organisms, which are naked flat masses 

 of protoplasm often several square inches 

 in area, provide ample material for chem- 

 ical analysis of the substance. (From 

 Sachs, Lectures.) 



