144 



The spleen tissue was ground up and a water extract was made. This 

 was purified by alcohol extraction. 



We have made a survey of different tissues of the rabbit in regard to the 

 recovery factor, and we found that the spleen contains more of this material than 

 any other tissue tested. It is possible that synthetic media other than the one 

 mentioned before may work also, but that we just do not have the right combina- 

 tion. 



KAMEN: Is there any pertinence to the idea of taking some of the postu- 

 lated precursors for DNA that are available and trying them, just inching up the 

 scale a bit? 



KAPLAN: Cole has done some of that work already. I imagine others 

 have done it too. With the purest DNA-protein preparations that he can get, for 

 example, by using low ionic strength extraction techniques, he gets very lovely 

 nucleoprotein which does not work. 



PATT: Will thymus extract facilitate the regeneration of thymus? 



KAPLAN: Thymus does not work. As I said, marrow is the only thing 

 that works. 



PATT: We have a situation here of blood-forming tissue rejuvenating 

 blood-forming tissue. However, thymus, which may be considered a part of the 

 blood-forming scheme, does not facilitate the recovery of its kind, i.e. , lym- 

 phoid or of other blood-forming tissues. 



KAPLAN: Well, It is more complicated that that. Actually marrow, as 

 you know, is an erythroid and, a myeloid tissue, and thymus is essentially a lym- 

 phoid tissue. Without getting into a discussion of blood formation, it is still 

 rather striking that myeloid tissue should cause regeneration of lymphoid tissue. 

 Well, in following that idea up (and Cole has done this too), we thought it would 

 be interesting to find out whether one could show that the activity is associated 

 with one or another cellular series in the marrow. If you inject turpentine sub- 

 cutaneously a sterile abscess is formed within Z to 4 days. This produces an 

 overwhelming myelocytic response in the marrow. This marrow, however, does 

 not have greater activity than ordinary marrow. 



The same is true if you use phenylhydrazine to produce transient anemia, 

 which causes tremendous erythroid hyperplasia in the marrow. Therefore, we 

 can conclude that the factor is not concentrated in the more nnature cells of eith- 

 er series, since neither an induced erythroid nor an induced myeloid hyperplasia 

 has a differential effect. I am not sure, but would suggest, at least, that the ma- 

 terial in the marrow is derived from a very primitive cell form that is not differ- 

 entiated along either line. That is a perfectly good lead, but we have not proven 

 it as yet. 



CURTIS: I am afraid our tinne is up and we must adjourn. I want to 

 thank all of you on behalf of the National Research Council for coming and par- 

 ticipating in this discussion. It has been a stimulating meeting and I hope each 

 of you has profited from it as much as I have. 



