384 PROTOPLASM 



Sen has observed the cataphoretic migration of particles in the 

 protoplasm of the petiole hair of Urtica and the root hair of 

 Azolla and finds them all to be negative. 



Protoplasmic Streaming.— The streaming of protoplasm is a 

 little understood phenomenon. Nearly all of the forces in the 

 physical world have been resorted to in attempts to explain it! 

 An electrokinetic interpretation is as reasonable as any other 

 and has the advantage of some experimental evidence in its 

 favor. The one-way protoplasmic streaming in the filaments of 

 bread mold is possibly an example of electroendosmosis.. The 

 protoplasm in the slender capillaries of bread mold flows many 

 seconds, or even minutes, in one direction only and then returns. 

 The first successful attempt experimentally to prove that such a 

 protoplasmic flow is an electrokinetic phenomenon was made by 

 Gelfan. He worked on the alga Nitella and was able to measure 

 the potential set up between the two ends of the long cell by the 

 streaming protoplasm. When the direction of streaming 

 reversed, the direction of flow of current, as indicated by a 

 delicate galvanometer, also reversed; and as streaming slowed 

 down until the protoplasm was quiet, the voltage became less 

 until it reached zero. We come to the inevitable, and usually 

 unanswerable, question, Is the potential the cause or the result 

 of the streaming? We cannot say, but it is of significance that a 

 change in potential is associated with a change in direction of 

 streaming. This Gelfan's work apparently proves. 



Stability. — Electrokinetic properties of nonliving colloidal 

 systems find application in the living world, usually without 

 modification. Now and then, certain seeming exceptions arise. 

 One of these is the stability of living particles. Joffe and Mudd 

 report living bacteria in suspension with zero charge in the normal 

 state. This may mean simply that potential as a stabilizing 

 agent is here replaced by another, probably hydration. A water 

 mantle is apparently in part responsible for the stability of 

 protein suspensions (page 177). Bacteria, which, though in 

 suspension, have no charge over the entire range of pH, probably 

 have carbohydrate in their surface, to the hydration of which 

 the suspension stability of the bacteria is due. 



Northrop and deKruif tell of an interesting fact which is well 

 known in nonliving colloidal systems. They have shown that a 

 low concentration of salt precipitates bacteria, while higher 



