ELASTICITY 231 



of sodium stearate (of the right quahty) with a viscosity value 

 but twice that of water will hold a minute metal particle in 

 suspension and exhibit a high stretching capacity, while a 40 per 

 cent sodium oleate solution, four hundred times as viscous as 

 water but wholly inelastic, will not (permanently) hold the 

 same particle in suspension. Two samples of sodium stearate 

 proved extraordinary in that, though presumably alike chemi- 

 cally, they exhibited quite different physical properties. (They 

 came from different manufacturers.) Freundlich and Schalek 

 had found that one of them deviated from Poiseuille's law of 

 true viscous flow, while the other obeyed it. The first proved 

 to be elastic, and the latter not. The elastic soap held a metal 

 particle in suspension even though the viscosity of the solution 

 was but twice that of water, while the inelastic soap required 

 a viscosity value of 31 times water to support the same particle 

 barely long enough to permit a hurried measurement to be made. 

 Their microscopic structural features also differed (page 226). 

 These facts teach us that deviation from Poiseuille's law (i.e., 

 anomalous flow), elasticity, and rigidity are usually concomitant 

 and that when one is absent, the other is also likely to be absent. 

 How general this rule is cannot be said, but it seems always to 

 apply to such gel-forming substances as soaps and the hydrophylic 

 colloids in general, including protoplasm. 



Elasticity, rigidity, and the related properties of contractility, 

 tensile strength, etc., are characteristic of protoplasm. Their 

 presence there can be experimentally proved. They indicate 

 that anomalous flow is also a characteristic of protoplasm. 



Protoplasm was early known to be elastic and sticky. The 

 first attempt at an accurate determination of one of its mechanical 

 properties was made by Pfeffer, who ascertained the tensile 

 strength of a strand of myxomycete protoplasm by attaching 

 weights to it and found that a strand measuring 0.3 mm. in 

 diameter would support 3.5 mg., which is 50 mg. per square 

 millimeter. 



The elastic qualities of protoplasm can be easily demonstrated 

 and measured with fair accuracy. When protoplasm is thin and 

 the extensibility correspondingly low, the presence of elasticity 

 cannot be readily shown, but there is no reason to assume that 

 it has therefore disappeared. The chemical constitution of the 

 dry weight of protoplasm is half protein; this indicates that 



