THE CELL. 



29 



Morbid cell reproduction is especially evident in neoplasms 

 and in hyperplastic formation. The type of reproduction in neo- 

 plasms is variable, being normal or modified, direct or indirect. 

 Indirect division is of most frequent occurrence in hyperplasia, 

 the rapidity of multiplication being the only apparent difference 

 from that occurring in normal reproduction. ;M1 variations of 

 division occur in tumors. 



Motion. — ^lotilitv is that property- of a cell which refers 

 either to the intracellular movement of its parts, the position of 

 the cell as a whole remaining fixed, or it signifies the inde- 

 pendent movement of the cell. All movement is dependent 



Fife', 1 1— Ciliated Epitlieliuu), Traciiea. 



upon activity of the cell protoplasm. The cells of specialized 

 tissues, except l)lood, are fixed i. e. not motile. 



Intracellular movement is due to the circulation or stream- 

 ino- of the protoplasm from one portion of the cell to another. 

 This type of movement mav become so extensive that the shape 

 of the' cell will be changed. It is common in the cells of lower 

 forms of life as well as in some of the cells of higner animals. 

 The specific cause of the intracellular protoplasmic circulation 

 has never been positively determined but it is probably the result 

 of ,a disturbed chemic equilibrium of the cell margins and their 



