114 CYTOCHEMISTRY OF PROTEINS 



work of this question. Two examples of these may be considered 

 as illustrations. One much publicised theory has been that the 

 nucleic acids serve as templates or moulds, upon which the pro- 

 tein is formed. So far as this theory implies that the surface of 

 a nucleic acid molecule can determine the sequence of amino 

 acids in a polypeptide chain, it seems to me quite naive, from a 

 physico-chemical point of view. To the extent to which the tem- 

 plate function is limited to determining the manner in which a 

 polypeptide chain is folded into a unique configuration there is 

 more to be said for this theory. A quite different alternative 

 theory is that the nucleic acids constitute a necessary part of the 

 environment in the same way that water does. Water is an 

 essential for protein synthesis, acting as a solvent, as part of the 

 protein structure, and possibly also as a catalyst and even as a 

 direct participant in the synthetic process; nucleic acid could, 

 so far as present knowledge goes, have a similarly essential role 

 as an environmental factor. 



The third question engenders a different set of enquiries. 

 The simplest approach to this problem is to suppose that the 

 places in cells which have the highest concentrations of protein 

 are the sites of synthesis. The intrinsic fallacy in accepting such 

 a hypothesis without proof may readily be seen if we consider 

 the somewhat broader scene of protein production in a country- 

 side: the highest concentrations of protein are to be found in the 

 slaughterhouses, cold-storage centres, and granaries, but the 

 actual sites of synthesis are the fields, pastures, and woodlands, 

 in which protein may be said, both literally and figuratively, to 

 be thin on the ground. Consequently, although it is of much 

 interest to discover and record the sites of occurrence of proteins 

 in cells, we must refrain from identifying the richer sites with 

 sites of synthesis until proof of this identity is obtained. 



With these considerations in mind, we may now proceed to 

 examine the problem in more detail. 



Caspersson's Cytological Systems 



First consider the observations connected with chromosome 

 reproduction. It was shown by studies on chromosomes, particu- 

 larly those of grasshopper spermatocytes, that the chromosomes 

 are richer in nucleic acid during nuclear division than at any 

 other time. This was interpreted as indicating "a connection 



