36 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



in parenchymatous or young growing tissues we may 

 find ninety-five per cent, of water. The phenomenon 

 of motion is common to all protoplasm. In plant 

 protoplasm a streaming process is manifest, which 

 shows considerable regularity as to the direction of 

 the current within the cell. This motion, as well as 

 physiological activities, is greatly modified by change 

 in temperature, and its activities are also very sen- 

 sitive to change in intensity of light and even to the 

 different colors of light as well as to the actinic rays. 

 It is therefore irritable in the highest degree. 



Cytoplasm is the name given to the protoplasm of 

 the cell body or that which surrounds the nucleus. 

 The cytoplasm exhibits (i) a fine reticulum of anas- 

 tomosing or interlacing threads or plates of vary- 

 ing complexity called spongioplasm or fibrillar mass. 

 These threads are probably composed of small par- 

 ticles or granules, named microsomes, that are in close 

 touch with each other and arranged in rows. The 

 other constituent of cytoplasm is (2) a fluid sub- 

 stance lying between the meshes of the spongio- 

 plastic reticulum, and has been called hyaloplasm, 

 paraplasm, or cytolymph. Recent observations in- 

 dicate that the microsomes are primarily derived 

 from the nucleus and constitute the more important 

 vital parts of the cell. 



In some cells the microsomes are so placed as to 

 give a foam-like structure to the cytoplasm rather 

 than a reticular appearance. Again, the cytoplasm 

 of certain cells has a homogeneous watery appearance 

 devoid of any definite structure. There are therefore 

 three theories as to the structure of protoplasm: 



