CHAPTER III 



ACTION OF THE DENSITY OF THE MEDIUM UPON 



PROTOPLASM 



IN this chapter we shall consider (I) the structure of proto- 

 plasm and the physiological action of solutions ; (II) the effect 

 of density upon the structure and general functions of proto- 

 plasm ; (III) acclimatization to solutions of greater or less 

 density than the normal ; and (IV) control of the direction of 

 locomotion by density-- tonotaxis. 



1. INTRODUCTORY REMARKS UPON THE STRUCTURE OF 

 PROTOPLASM AND THE PHYSICAL ACTION OF SOLUTIONS 



It is now generally recognized that protoplasm consists of 

 two substances closely interwoven : the living plasma and a 

 watery chylema. The relation of the plasma and the chylema 

 is still a debated matter. Since the only theory of the struct- 

 ure of protoplasm which has been experimentally tested is that 

 of BUTSCHLI, his theory is especially worthy of recognition. 

 According to this theory, the relation of plasma and chylema is 

 that of water and air in a foam-work. The whole protoplasmic 

 mass is bounded and penetrated through and through by plasma 

 films which envelop watery globules. It is with membranes 

 constructed of such protoplasm that the physical phenomena 

 of osmosis are exhibited.* 



Osmosis occurs when two aqueous solutions of different 

 density are separated by an animal membrane. f Such a mem- 



* Excellent treatises on the physical and chemical nature of solutions, in- 

 cluding a discussion of osmosis, are : OSTWALD, '91, and WHETHAM, '95. 



t Osmosis occurs likewise when such solutions are separated by inorganic 

 walls containing pores of extreme fineness ; e.g. a wall of porous clay in which 

 copper ferrocyanide has been precipitated. 



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