14 INTRODUCTION PKOTOPLASM CELL 



(Amer. Jour. Phys., 32, 2, 1913) of the physical properties and molar struc- 

 ture of protoplasm in various cells, by combined methods of microdissection 

 and vital staining, have led to clearer conceptions in this field. Kite ac- 

 cepts the interpretation of protoplasm as an emulsoid, the real structural 

 units of which are the colloidal particles ; and he con- 

 ceives of the optical image as the result of the com- 

 bination of the physical phenomena of reflection, re- 

 fraction, diffraction, absorption, dispersion, interfer- 

 ence, and a scattering action on light. Living proto- 

 plasm is an apparently homogeneous and viscous 

 hydrogel, holding in suspension in the form of gran- 

 ules ('microsomes') minute masses of denser gels, and 

 liquid globules ('alveoli') which show many of the 



optical properties of an oil drop. The 'network 7 and 

 JIG. 19. COLUMNAR , , . ^ - Tr . J -, n 



CILIATED EPITHE- granules' of the nucleus Kite regards as optical phe- 



LIAL CELLS, SHOW- nomena, areas of greater concentration in the nuclear 

 ING CANALICULAR gel, not separated from, but grading into the sur- 

 APPARATUS. rounding diluter gel of the 'nuclear sap.' Spindle 



After Holmgren. fibers were successfully dissected out of the proto- 

 plasm as distinct, relatively rigid threads. These con- 

 clusions are in the main in accord with those deduced from the earlier 

 physiochemical studies of protoplasm and colloids by Hardy and others. 

 M. R. and W. H. Lewis (op. cit.) also find no sign of a reticular or of an 

 alveolar structure in either cytoplasm or nucleus in cells studied in tissue 

 cultures. They describe both cytoplasm and nucleus as 'finely granular 

 almost homogeneous in appearance.' 



VITAL PROPERTIES OF CELLS 



Living protoplasm is capable of certain specific reactions (physiologi- 

 cal processes) or functions. These reactions are spoken of as vital prop- 

 erties or attributes of protoplasm. They are general properties of living 

 matter. They include primarily (1) metabolism; (2) irritability; (3) 

 contractility; (4) reproduction. 



(1) Metabolism. Metabolism is that property of living proto- 

 plasm by virtue of which it can elaborate from raw food material the 

 complex chemical compounds of protoplasm (anabolic phase, construc- 

 tive metabolism, assimilation), and convert the same into kinetic energy 

 for the performance of specific functions (katabolic phase, destructive 

 metabolism, dissimilation), e.g., secretion and excretion. Metabolism 

 generally involves growth and differentiation. Development also is 



