1920] SEI FRIZ— PROTOPLASM 



373 



Rhizopus 



opus (anc 



we have, as 



xom) 



changing from one to the other with changes in physiological 

 activity. The protoplasm in the hyphae of bread mold, in the 

 quiescent state, is of very high consistency. It possesses the 

 greatest viscosity of any living plant protoplasm which I have 

 observed by the aid of microdissection. 10 It is of gel consistency, 

 more usually that of a soft gel (v. v. 9), is sticky, quite elastic, 

 and very extensile, closely resembling bread dough in these physical 

 properties. At times it exhibits some resiliency, and may then be 

 characterized as a rigid gel (v. v. 10). Kite (15) has described 

 the living substance of the striped muscle cell of Necturus as "the 

 most viscous, elastic, and cohesive of the living gels we have so 

 far considered." The protoplasm of the cells of nerve and muscle 

 tissue is probably of as high a viscosity as any living animal plasma; 

 but it must not be concluded from these observations that this 

 gel consistency is necessarily permanent. Nerve and muscle 

 protoplasm probably exist, just as all the protoplasm so far con- 

 sidered exists, in the sol state at times. Indeed, certain theories 

 of muscle contraction based on "a temporary redistribution of the 

 more fluid portion of the tissue" (Lillie, 18), and on " coalescence 

 (incipient coagulation) of colloidal particles," which is reversed 

 during the relaxation phase (17), demand a varying viscosity of 



muscle cells. 



Ordinarily, when a filament of bread mold is torn the inactive 



asm 



a 



some distance back from 



can be forced out in the form of a rod, just as one would squeeze 

 oil paint from an artist's tube, and this rod maintains its shape 

 until disturbed. 



The streaming protoplasm of Rhizopus, as one would expect, 

 is considerably less viscous than the quiescent protoplasm, but it 



JO The viscosity of plant protoplasm which is undergoing long periods of rest, 

 for example, that of seeds, is undoubtedly of even greater concentration, for here 



the water content is reduced to 20 per cent, while in protoplasm in which pronounced 

 metabolic processes are going on the percentage of water is 80 or more. 





