CELLS 



31 



42. General Physiology of the Cell. — There is a division of labor in the 

 cell among the structures which have been named. The nucleus is, in a 

 sense, the vital center. Cytoplasm alone is unable to carry on all vital 

 activities and its life is brief after it is separated from the nucleus. Prob- 

 ably under the influence of substances formed by the nucleus and passed 



Fig. 8. — Various types of cells. A, epithelial cell shed from the lining of the human 

 mouth; a is a side view of the cell. X 300. B, human egg cell, nearly mature. X 200. 

 C, motile human sperm cell. X 1300. D, diagram of a nerve cell. E, a bone cell; some- 

 what diagrammatic. X 700. F, human blood corpuscles. X 1000. G, nonstriated 

 muscle cell from mammalian intestine. X 640. 



out into the cytoplasm the latter does most of the ordinary work of the 

 cell, including the taking in of food, the carrying on of many of the chemi- 

 cal and physical changes associated with life, the passing out of waste, the 

 reception of all stimuli, and the movements which occur in response to 

 them. The chromatin is the medium by which hereditary characters are 



