162 L. J. MULLTNS 



can see in the microscope, that gives you an oil phase. There is no such thing 

 as an absolutely hydrophobic lipid. In fact, they are amazingly hydrophilic. If 

 you take, for instance, brain lipids, you can make a suspension in water just by 

 making enough water. Furthermore, just try to get water out of brain lipids, 

 for there is nothing in brain lipids except the oils. 



Another thing is the fact that the more we know about tissue chemistry, the 

 more we come to realize that most proteins and most lipids — structural ones, I 

 am talking about — are tied into lipo-proteins of different size, different proper- 

 ties and different constitution. What this means in terms of the intimates is that 

 wherever you have a lipid, presumably hydrophobic area, you get very close by, 

 a hydrophilic, presumably protein layer. Therefore, I don't see how you can 

 escape the fact that you have to deal with a mosaic. Of course, you would have 

 the orientation that Dr. Schmitt and his workers have shown in which 

 you would have a lipo-protein which would present only its paraffinic chains 

 or its protein framework as the case might be. I think that when you are dealing 

 with a membrane it would be another proposition altogether. 



Then, one thing I must protest vehemently against is the idea of considering 

 the membrane a mechanical thing, as a thing that does not change. It seems to 

 me that most permeability phenomena are products of many events which are 

 going on inside and outside and those sequence of events meet at the area of an 

 interface. I think it is perfectly normal to assume that the structure of the mem- 

 brane is very likely to change from one physiological condition to the other. 

 I wonder if anybody has any comment on that. 



Dr. Davies: When I used the word "oil" I meant lipid, an oriented lipid, 

 which would, I think, meet your requirements. I have no objections to all kinds 

 of things happening at a lipid-protein interface, which would be in line with 

 your statement that there have to be changes going on in order to allow perme- 

 ability changes to take place. 



Dr. Burton: I wanted to ask for a little more speculation from Dr. Mullins 

 on the property of his holes. He has been speaking so far about these agents 

 sitting on top of the membrane and blocking the hole. I wonder if he would care 

 to speculate a little more on the property of the holes themselves, that is, insofar 

 as there are varying sized holes for varying sized molecules. Are the polar groups 

 sticking into the holes from the protein different in different holes to account 

 for a certain amount of specificity? In this respect I presume we are speaking 

 of simple diffusion, and I wonder if he would care to speculate on the property 

 of these holes and the function of active transport perhaps an enzyme on the 

 inside surface of these holes transporting the material inside. 



Chairman Gerard: It seems to me that temperature would be an enormously 

 valuable tool in getting at an analysis of this since the effective size of the holes 

 is, according to this theory, directly a function of temperature. Also the rate at 



