STRUCTURE OF NERVE CELL MEMBRANES 163 



which a molecule gets through this long column would be influenced by the 

 thermal oscillations of the protein columns which every so often ought to clamp 

 down on it (the frequency for the pulsing of the hole versus the linear move- 

 ment of the molecule). It might lead to some interesting temperature predic- 

 tions. 



Dr. Mullixs: In the case of Dr. Gerard's question about temperature effects, 

 I agree that this is really a most useful method for further investigation. One 

 would predict on this basis that if you raised the temperature too high and ex- 

 panded this lattice structure, you weaken the inter-molecular attractive forces 

 of the membrane and some point will be reached where at one locus or another 

 this force will be so attenuated between the molecules that you get effectively 

 a breakdown or depolarization at that point which will, of course, cause a propa- 

 gated disturbance and so high temperatures would be excitatory. If you lower 

 the temperature you must expect an inverse effect, a decrease in the mean hole 

 size, but also the possibility exists that the same kind of a crystallization that 

 was produced by chemical agents is now produced by the lowered temperature, 

 so that at one site or another you get again a disturbance which will result in 

 depolarization and, therefore, in a propagated conduction. This would require 

 rather special conditions, but it does explain the fact that there are both cold 

 and hot receptors, both of which give stimulation in response to temperature 

 changes up or down from some fixed point. 



I must say that we were somewhat guided in these thoughts by the notion 

 that the very precise temperature control which the mammalian organism is 

 subject to could very conveniently be arranged by having an equilibrium exist- 

 ing in a membrane between melted and frozen parts such that any change in 

 the distribution of such sites would cause stimulation, in other words, a ther- 

 mostat, if you like. It would be easy to think of other mechanisms for a thermo- 

 stat if the temperature regulation were not absolute. That is to say, the tem- 

 perature regulation is absolute sometimes to as good as a tenth of a degree 

 centigrade, a very small change on an absolute scale, and yet it always is at 

 this particular value. Mechanisms involving viscosity changes and so on in 

 the cells which might be expected to be as sensitive, but not in an absolute 

 way, would fit in with this notion that Dr. Gerard suggests about temperature 

 effect. 



Chairman Gerard: Before you leave that, you have not picked up the par- 

 ticularly critical part of this, as I see it; namely, at a lower temperature the 

 average size of the hole should be decreased somewhat and you should get a 

 markedly differential action on your larger versus your smaller molecules in 

 changing the excitatory and the narcotizing effects. Is that correct? And, if so, 

 is there any evidence to support it? 



Dr. Mullins: I cannot say for the lower temperatures. It is a fact, however, 



