DIFFUSION PROCESSES IN HUMAN HAIR 607 hair which readily takes up dye and is readily permed, have holes of different size from hair resistant in these respects ? THE LECTURER: I have a little evidence on the behaviour of permanently waved hair compared with ordinary hair, which may partly answer your question. We have Fig. 2 showing against the radius of the dye, with Italian hair. If we permanently wave this hair, we have a little data indicating a line with a steeper gradient but intercepting at about the same place. This means that the radius of the hole in permanently waved hair is not significantly different, but that the number of the holes is higher. DR. J. F. CORBETT .' In the experiments relating to the rate of uptake of dye, was there any significant difference between the graphs obtained for amount taken up against time for the three small dyes, C, D and E, com- pared with the much larger dyes A and B of presumably much higher affinity for the fibre ? I cannot help feeling that A and B will be rapidly absorbed on to the surface, and being much larger molecules, will link not only by salt links, but by Van der Wals forces, providing themselves by surface absorp- tion a barrier to further absorption of the dyes. Do the rate uptake curves indicate anything like this ? THE LECTURER: The rate of uptake curves show slower uptake with the: larger molecules. DR. J. F. CORBETT ' Is there a break in them ? THE LECTURER .' In general, they were smooth curves not showing any great discontinuity. You must remember that we washed quickly in order to get rid of anything that was loosely adhering to the outside, because we were not interested in material which is just absorbed on the surface. DR. J. F. CORBETT: I asked this question because you stated in your preamble that you were trying to determine whether hole size had any effect or not. I cannot help feeling that the affinity of the dyestuffs, differing so very widely, particularly in respect of molecular size, may be responsible for the different rates of diffusion rather than the radius of any holes. I feel that one might get nearer to ideal conditions by using a series of sulphonic acids with no other substituents rather than the dyestuffs that you used. THE LECTURER: I have used these particular dyestuffs because the, organic chemists in my laboratory have not managed to make the molecules which I want, and I wanted to determine if the general idea was correct while they were making them. We want spherical molecules, or as near spherical as possible, all with the same reactive group, which gradually gets bigger. When thinking about this, you find it is almost impossible. While I agree

608 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS with you that this could be a weak point, it has not worked that way in fact, and the highest reactivity ratio obtained (which is an indication of affinity) was with azobenzene psulphonic acid, and was very much greater than with some of the much larger molecules. DR. H. G. TROTH: I would like to invert this experiment. Could you choose a single molecule and alter the hole size, and then use the molecule as a measure of the hole size of a particular level ? THE LECTURER: I would have thought that permanent waving would have altered the hole size. But apparently it does not. I do not know how to alter the hole size. PROE. C. S. WHEWELL: What do you really mean by hole size ? At what level of organisation do you believe these holes exist ? What relation do these holes have to microfibril structure, protofibril structure and the rest of it ? THE LECTURER: I am not sure whether the holes are within the helices, in which case the whole thing gets distorted, or whether they are between the helices. What do you think ? PROF. C. S. WHEWELL: It would appear to be quite a critical experiment to repeat your work on hair which is stretched by 30% and held stretched. This would alter the disposition in one direction. THE LECTURER: It is a good idea, and it helps Dr. Troth by varying the size of holes.