INTRODUCTION 3 



countered with artefacts due to fixation. This matter was 

 brought to a head by W. B. Hardy and A. Fischer in two publi- 

 cations in 1899. These two investigators had a much clearer 

 understanding of the physical basis of cytological techniques 

 than had most of the previous workers in this field. They 

 showed that the details of the procedure of fixation, of the 

 nature of the fixative, and the technique of staining, have just as 

 profound an effect upon the final picture as has the initial 

 chemical composition of the material being stained. They also 

 showed that many of the fixatives in common use were giving 

 rise to structures which, in fact, did not occur in the living 

 cells, but were precipitation artefacts. At this time, neither the 

 chemistry nor the physics of the systems involved in cytology 

 were sufficiently understood for it to be possible to cope with 

 the problems demonstrated by Hardy and Fischer. Conse- 

 quently, by 1910 the wave of interest in the study of fixed 

 preparations had very largely lost its momentum so far as pio- 

 neering investigations were concerned. The pioneering investi- 

 gators instead turned to working on living cells almost exclu- 

 sively. There was, in consequence, a very rapid development 

 of experimental cytology. 



Between 1910 and 1935 remarkable progress was made in the 

 field of experimental cytology. Some phenomena were so suc- 

 cessfully analyzed that the chief physico-chemical factors in- 

 volved could be detailed, and given an approximate mathemati- 

 cal treatment. However, the result of this successful investiga- 

 tion was that many of the working hypotheses formulated by 

 the experimental cytologists postulated specific cytochemical 

 organisations in particular parts of cells. Such postulates were 

 found in many widely diverse fields, e.g., ciliary and amoeboid 

 movement, muscular contraction, secretion, and the action of 

 genes. The postulated cytochemical organisations lay so fun- 

 damentally at the heart of the mechanisms proposed that further 

 progress was bound to become increasingly limited in every 

 field, unless further advances were possible in cytochemistry. 

 It is not surprising, therefore, to find that from 1935 onwards 

 there was a renewed wave of interest in cytochemistry. Land- 

 marks in this new wave of interest were the publication of 

 Lison's book "Histochimie Animale," and the papers of Feulgen, 

 Caspersson, Gomori and Takamatsu, Linderstr0m-Lang, and 



