170 General Discussion 



animals with tissues of different ages. For completeness' sake, I think 

 one should add parabiosis, which Prof. McCay mentioned yesterday. 



I'd like to show you a concrete example of the use of what Krolm 

 described as "delayed autografting". Billingham and I have been 

 studying the storage of skin mainly for this purpose. The principle of 

 delayed autografting, as Parkes explained, is the removal of tissue from 

 a young animal and its transplantation back to the same animal when 

 it is a bit older. Fig. 1 shows a raw area prepared on the chest wall of a 

 rabbit which is five-hundred days old. It has four grafts on it, which 

 have been in position for eight days. As you see, two of the grafts are 

 pale, and two of them are rather black. The two darker grafts were 

 removed immediately the animal was born, and stored at the tempera- 

 ture of dry ice after soaking in glycerol-Ringer. The two whiter grafts 

 were removed only one day before the grafting operation. They were 

 soaked in glycerol-Ringer, frozen to the temperature of dry ice for 

 twenty-four hours, and then thawed out again. The four grafts were 

 then transplanted simultaneously. One can see from the picture that 

 the four grafts have survived and are surrounded by about the same 

 amount of new epithelial outgrowth. (Outside the raw area are two 

 "fitted" grafts, one young and the other of the same age as the host: 

 these have healed perfectly but are not, of course, surrounded by out- 

 growth.) Billingham and I started quite a number of experiments of 

 this type, but we are now running into a difficulty which Parkes has 

 called attention to, namely deterioration on storage. The longest period 

 which we have so far been able to keep newborn skin in storage is seven- 

 hundred days. After that period the epithelium is still viable. But an 

 experiment of this sort, which is designed to discover the behaviour of 

 young skin in an old environment, is obviously vitiated if there is any 

 degree of deterioration on storage at all. At seven-hundred days, and 

 still more so in a very recent experiment witlr grafting new-born skin 

 after eight-hundred days' storage, there is unfortunately a quite con- 

 spicuous deterioration. For example, the melanocytes, which confer 

 the pigmentation on the young grafts (rabbits are born very dark) have 

 pretty well disappeared. So although this is a technique of great poten- 

 tial promise, I am afraid we may be severely handicapped by the fact 

 that one does, as Parkes has pointed out, get progressive deterioration 

 on storage. 



Parkes: I think what is wanted is some more work. We have to deal 

 with one problem after another as it comes up. Four years ago we 

 couldn't preserve any of the cells in which we were interested for any 

 worth- wliile length of time. Gradually the conditions required for each 

 different kind of cell or tissue, conditions which may be totally different, 

 have been worked out. Unless you have already tried a large range of 

 media and temperatures and methods of freezing and thawing, it is 

 premature to say that the skin won't last at a low temperature. 



Medawar: You think that for each tissue it will be possible to find a 

 medium in which biopiiysical deterioration on storage won't occur? 

 Are you prepared to go on record as saying that? 



Parkes: I'm prepared to go on record as saying that I have no doubt 



