14 M. H. F. WILKINS 



may be prepared which consist of aggregates of parallel microcrystals. 

 With care in producing the DNA (by Dr. L. D. Hamilton of the Sloan- 

 Kettering Institute, New York) and by taking pains with the diffraction 





Fig. I. X-ray diffraction photograph of microcrystalline fibres of the Hthium 

 salt of DNA. 



technique we have gradually improved our fibre diffraction photographs, 

 and such is their sharpness now that overlapping of reflections is to a large 

 extent avoided (Fig. i.) As a result we are able to separate a large proportion 

 of several hundred reflections in three dimensions and obtain a reasonably 

 accurate set of intensities. We have also reduced the difficulty of limited 

 resolving power of the data. We have recently increased the resolving 



