58 



THE CELL AND PROTOPLASM 



hereditary substance, has only recently been 

 attacked by Caspersson and Schultz. They 

 find significant changes in the quantity of 

 nucleic acid paralleling certain genetic and 

 cytological facts. They conclude therefore 

 that the nucleic acid is concerned with the 

 function and the reproduction of the gene, 

 the latter process being a polymerization 

 followed by depolymerization. (The value 

 of these conclusions is unfortunately im- 

 paired by the unproved and improbable 

 assumption that the mottling effect of the 

 eyes, which furnishes the genetic material, 

 is the result of a loss of genes in develop- 

 ment.) 



The most important problem, however, 

 has not yet been attacked by direct chemi- 

 cal methods, namely, that of the constitu- 

 tion of the gene-string. The classic theory 

 requires a string of many hundreds of dif- 

 ferent units, each of which is at least of 

 the order of one molecule, and of a sub- 

 stance different from that of all the others ; 

 these molecules must be held in place by 

 some structure. It ought to be possible to 

 prove or disprove such an assumption. An 

 old and recently revived modification of the 

 classic theory assumes that the gene-string, 

 or chromonema, is a single giant chain mole- 

 cule to which all the genes are attached as 

 sidechains (Castle, Renner, Koltzoff, De- 

 merec). Improbable as such an idea is, 

 as well from a genetical as from the chemi- 

 cal point of view, it might be possible to test 

 it. But it is also possible, as we shall see 

 later on, that the chemical constitution of 

 the proteinic core may be considered as a 

 single unit of definite stoechiometric prop- 

 erties along its axis, i.e., a giant chain mole- 

 cule or a micellar bundle of such molecules 

 with no room left for individual genes. All 

 these and eventually other possibilities 

 ought to become accessible sooner or later 

 to an attack with the ingenious methods now 

 available, and cytologists and geneticists 

 will have to adapt their ideas eventually to 

 the findings of the physicist and chemist. 

 Personally I am convinced that the solution 

 of this all-important problem will be has- 

 tened if the physicists and chemists working 

 in this field will stop looking for particulate 



genes, of molecular (or even submolecular) 

 order, the very existence of which is becom- 

 ing more doubtful daily, as we shall see 

 further on. 



In this connection, I should like to draw 

 the attention of those who wield the physico- 

 chemical tools for an attack upon our prob- 

 lem to a remarkable cytological fact which 

 is generally disregarded in the discussion of 

 our problem. At the time when I was my- 

 self a staunch adherent of the classical 

 theory of the gene, I was always puzzled by 

 the fact that the chromosomes of all ani- 

 mals and plants, including Protozoa and 

 Protophyta, which show clearly visible chro- 

 mosomes, are very much alike. Whatever 

 small differences exist, in all decisive points 

 the completely stretched chromosomes are 

 alike in structure as well as in the order of 

 magnitude of their dimensions. I might 

 put a slide of the chromosomes of the pro- 

 tozoan Monocystis (Gregarina) side by side 

 with slides of some animals and plants and 

 no one could point out any essential differ- 

 ence. Since the days of Roux it is assumed 

 that this type of threadlike chromosomes 

 takes its raison d'etre from the necessity of 

 exact division of the material of heredity. 

 The theory of the gene is based upon ex- 

 actly the same point of view. Therefore, 

 there would not be any sense to the fiber- 

 like form of the chromosome if its length 

 were not roughly proportional to the num- 

 ber of genes therein. Actually the well- 

 known maps of the Drosophila chromosomes 

 bear witness to this conclusion. From this 

 we must conclude that the number of genes 

 is approximately equal, as far as order of 

 magnitude is concerned, in some chromo- 

 somes all over the animate world. This 

 puzzle disappears completely if the chromo- 

 some itself is a chemical unit which may 

 show any amount of differential chemical 

 complexity in different chain molecules of 

 similar length. 



These last remarks lead to the next chap- 

 ter of our discussion. If chemical investi- 

 gation has not yet furnished anj^ informa- 

 tion regarding the so-called gene-string, 

 what other information can we derive from 

 experimental facts ? As everybody knows — 



