PROTOPLASM AND COLLOIDS 



1!)8 



Tn tlie first place, let ns consider some ex- 

 periments ^vith ameba. If ameba is sub- 

 jected to vdti-a\ioiet radiation, there is an 

 immediate licpiefaction of the cortex or 

 phisma-el. As Ano^erer (1936, 1937) has 

 shown, similar liquefaction follows mechan- 

 ical impact or electrical shock (Fiiz. 4). 



II 1^ IJ 14 15 [<, ^ 17 18 19 

 ACiTATlON Tint IN MinuTES 



Fig. 4. Effect of mechanical agitation on the vis- 

 cosity of the plasmagel of Amoeba proteus. Ordi- 

 nates show relative viscosity, abscissae the time of 

 agitation (after Angerer). 



Further evidence for the release of calcium 

 following stimulation is shown by the ex- 

 periments of Mazia and Clark (1936) on 

 Elodea leaves. These cells are conveniently 

 provided with oxalate salts dissolved in 

 their vacuoles, and this oxalate serves as an 

 indicator for calcium. No matter how the 

 Elodea cells are stimulated — -whether with 

 electric or mechanical shock, or with ultra- 

 violet radiation — calcium is released from 

 the protoplasm, enters the vacuoles, and 

 forms readily detectable calcium oxalate 

 crystals there. 



But to return to the ameba. I have 

 pointed out that when the ameba cell is 

 stimulated, the cortical plasmagel acts as if 

 it had lost calcium. On the other hand, the 

 plasmasol, that is to say, the protoplasm of 

 the ameba interior, behaves as though cal- 

 cium had entered it. Following irradia- 

 tion with ultraviolet, there is a transitory 

 liquefaction of the plasmasol such as nor- 

 mally occurs following the addition of a 

 very small amount of calcium ion. Im- 

 mediately thereafter there is a sharp vis- 

 cosity increase, indicative of protoplasmic 

 clotting. Exactly similar changes follow 

 other types of stimulation. 



Onr results with ameba thus indicate that 

 following treatment with any type of stimu- 

 lating agent, calcium is released from the 

 cortex, enters the cell interior and produces 

 a species of clotting there. Thus there are 

 two asjiects of the response to stimulation 

 — first, the release of calcium from the cor- 

 tex, and second, the effect of calcium in 

 producing clotting. 



Recently we have been able to consider 

 at least one phase of excitation in another 

 type of protoplasmic system, the egg of the 

 worm Nereis. When this e^xg is shed into 

 sea-water, it has a large intact nucleus or 

 germinal vesicle. This remains intact un- 

 less the egg is fertilized or artificially stimu- 

 lated in one way or another. Such stimu- 

 lation may, for example, be accomplished 

 by ultraviolet radiation or by isotonic solu- 

 tions of sodium or potassium chloride. If 

 the eggs are subjected to the radiation from 

 a mercury vapor lamp, a few seconds ex- 

 posure may be sufficient to cause a complete 

 disappearance of the nuclear membrane. 

 It will be remembered that in most cells 

 breakdown of the nuclear membrane is a 

 necessary preliminary to mitosis. 



Experiments with Nereis eggs have 

 shown that stimulation by ultraviolet radi- 

 ation may be prevented if the eggs are first 

 immersed in sodium citrate solutions for 

 five to six miiuites. The citrate solution 

 presumably removes calcium from the cell 

 cortex and the egg becomes insensitive. 

 The egg is not killed or severely injured 

 by the citrate treatment, for on return to 

 sea water it regains its sensitivity to ultra- 

 violet radiation. Similar experiments can 

 be performed with sodium chloride or po- 

 tassium chloride solutions. These too lose 

 their effect if they are tried on eggs pre- 

 viously immersed in citrate solution. This 

 is in line with experiments which indicate 

 that sodium or potassium may release cal- 

 cium into the cell interior. Unfortunately 

 I have no time to refer to these experiments 

 in further detail. 



In a very brief and incomplete fashion, 

 I have outlined a theory of stimulation in 

 terms of protoplasmic effects, and I have 

 tried to present some of the evidence in 

 favor of this theorv. Now the value of an.y 



