34: H. COTTIER, E. P. CRONKITE, E. A. TONNA, AND N. O. NIELSON 



Crathorn, 8th Congr. Europ. Soc. Haematol., Vienna 1961), but there is little additional 

 information. Intestinal epithelium obtained by biopsy from sprue-patients and incubated 

 in vitro with tritiated thymidine in some instances did not label (Cronkite and KUlmann, 

 unpublished data). This may be another example of cells being unable to incorporate 

 tritiated thjanidine into their DNA. 



devik: The differences quoted by Dr. Cottier between his results and Dr. Lisco's results 

 with respect to the dose may not be as large as they seem. We injected a series of mice 

 with different amounts (I fic/g tritiated thymidine or 10 jjLc/g) and measured the total 

 amount of activity. This was not ten times higher in the second group; it was quite 

 variable in different organs, within the gut it was almost ten times as high but in most 

 tissues it was much less. It may be possible that the dose difference is smaller, and one 

 more point which Dr. Gray mentioned is that with a higher dose you may kill all the 

 cells. We think this is apparent from other results. 



cottier: We do not know as yet what degree of cell death was caused by the admmistra- 

 tion of tritiated nucleosides in doses such as those given in our experiment. It is not 

 excluded that the lack of increased leukaemogenesis after this treatment may, at least in 

 part, be due to a disintegi'ation of labelled cells. On the other hand the statistical 

 significance of the tumorigenic action Lisco's group obtained with the injeccion of only 

 1 fxG tritiated thymidine per g body weight (specific activity 360 mc/m mole) is open to 

 criticism. 



