112 The Structure of Protoplasm 



pentose may be removed without affecting the continuity of struc- 

 ture." Since the protein of the chromosomes was not digested by 

 pepsin, they consider that it may be related to the protamines or 

 histones. The molecular structure of the chromosome which these 

 authors support is one of long polypeptide chains and parallel nucleic 

 acid molecules. Experiments with polarized light and X-ray diffrac- 

 tion studies reviewed by Frey-Wyssling (1938) and Schmitt (1940) 

 suggested the assumption of parallel structure and are, like Mazia 

 and Jaegar's data, against earlier concepts of a warp-and-woof fabric. 

 Caspersson (1936) observed that the nucleic acid content is 

 increased shortly before cell division, and after cell division it 

 decreases again. Later (1939), he showed that in grasshopper sper- 

 matocytes, nucleic acid "synthesis" is completed, i. e., the maximum 

 amount is reached, before "maximum condensation of the chromo- 

 somes." Since nucleic acids are present in large amounts before cell 

 division and evidence from other studies on the submicroscopic level 

 indicates that the self-reproducing viruses and phages also contain 

 appreciable amounts of nucleic acid in their molecules, an attempt 

 is made to correlate these data with observations from the second 

 level. Here trouble begins — or so at least it seems to me. The 

 generalization is first made that nucleic acid concentration is at a 

 maximum in the nucleus at about the same time as the chromosome 

 is believed to reproduce itself, and from this the conclusion is reached 

 that nucleic acid is fundamentally connected with gene reproduc- 

 tion. This is a plausible and, I should think, even highly probable 

 hypothesis. But, how is it supported by microscopic data? The 

 latter deal with chroviosome reproduction or "splitting," and there 

 is much evidence against and little in favor of the view that this is 

 the same thing as gene reproduction. As Caspersson points out, 

 chromosome "splitting" cannot be seen until there has been an 

 accumulation of nucleic acid, for it is this which stains. He says, for 

 this reason, that the observation of chromosome splitting in very 

 early prophase says nothing against the view that nucleic acid 

 formation and gene reduplication go together. But is it not also 

 reasonable to conclude that the association he has found says noth- 

 ing definitely for it? In itself the observation that nucleic acid con- 

 centration is at a maximum near the time that chromosome splitting 

 becomes obvious may mean nothing more than that nucleic acid con- 

 centration permits doubleness of the chromosome to be seen. How- 

 ever this may be, the attempted first and second level correlation runs 

 into further difficulties. The first of these is that descriptive 



