190 BO THORELL 



Wyckoff et al.,^^ both confirming the earlier observations of Kohler and von 

 Schrotter. Wyckoff et at. also commented on the similarity between the 

 ultraviolet photomicrographs and those of Feulgen-stained preparations. 



The ultraviolet absorption of the chromosomal nucleic acids was dis- 

 cussed in a paper by Caspersson, E. and H. Hammarsten" in 1935, in which 

 they showed that chromosomes from Stenobotrus testicular cells did not 

 change their absorption at 280 m;u after digestion with trypsin-lanthanum 

 reagent. Similar results were obtained on the bands of Drosophila giant 

 chromosomes, and the authors concluded that these structures contained 

 large amounts of nucleic acids. 



From this time onwards many cell-physiological problems concerning 

 the nucleic acids were studied with the help of ultraviolet microscopy by 

 the Stockholm group^^ and also by a group at King's College, London." 

 It has been made quite clear that the techniciue has important biological 

 applications. But theoretical as well as practical experience has shoAvn that 

 the optical and physicochemical properties of the common cytological ma- 

 terial, and also the optical conditions in the microscope, are factors not 

 yet completely understood. Consequently, the quantitative analytical ap- 

 plication of ultraviolet microscopy is somewhat complicated if vahd results 

 are to be obtained. Recent discussions of these questions can be found in 

 papers by Glick et alJ^ and Davies and Walker.^' The analytical procedure 

 also involves the necessity for strictly defined conditions as regards tech- 

 nical equipment, and references are here made to some pertinent 

 papers.*'''*^ This question is also discussed in some detail in Chapter 17. 



For chromosomal analysis with ultraviolet microspectrography, the 

 giant chromosomes from Drosophila larvae have frequently been used. 

 From a topographical point of view, these chromosomes have certain ad- 

 vantages since they represent very much enlarged nuclear structures of 

 haploid type formed by endomitotic division and pairing. The different 

 parts of the chromosme consisting of euchromatin, heterochromatin, cer- 

 tain gene loci, etc., can with certainty be cytologically defined.^^'^^ Analysis 



" R. W. G. Wyckoff, A. H. Ebeling, and A. L. Ter Louw, /. Morphol. 53, 189 (19?2). 



^« T. Caspersson, "Cell Growth and Cell Function." Norton, New York, 1950. 



" see J. T. Randall, Discussions Faraday Soc. 9, 353 (1950). 



'8 D. Glick, A. Engstrom, and B. G. Malmstrom, Science 114, 253 (1951). 



^s H. G. Davies and P. M. B. Walker, Procjr. Biophys. and Biophys. Chem. 3, 195 



(1953). 

 8° T. Caspersson, J. Roy. Microscop. Soc. 60, 8 (1940). 

 8' B. Thorell, "Studies on the Formation of Cellular Substances during Blood Cell 



Formation." Henry Kimpton, London, 1947. 

 82 B. Thorell, Discussions Faraday Soc. 9, 432 (1950). 

 8» M. Wilkins, Discussions Faraday Soc. 9, 363 (1950). 



8* R. Barer, E. Holiday, and E. M. Jope, Biockim. et Biophys. Acta 6, 123 (1950). 

 85 R. Mellors, Discussions Faraday Soc. 9, 398 (1950). 

 8« T. Caspersson, F. Jacobsson, and G. Lomakka, Exptl. Cell Research 2, 301 (1951). 



