210 SECTIONAL ADDRESSES. 



denoted by the innocent -looking symbol \50, If, instead of all being 

 different, one kind of link recurred ten times, the number would be reduced 

 to [50 / [10. If, in addition, there were four that recurred four times and 

 ten that recurred twice, it would be further reduced to 



\^l\^x{\LYx{il_Y\ 



It would now consist of a chain of only fifty links, of which there were 

 only nineteen different kinds, and the number of different arrangements 

 of its parts would be about 10". Astronomy deals with big figures. 

 Light, it is said, takes 300,000 years to travel from one end of the Milky 



Way to the other ; this distance expressed in Angstrom units, 10,000,000 

 of which go to a millimetre, would be less than 10*^ So far are we from 

 knowing the structure of protein molecules. So far are we from knowing 

 what variations in disposition of the parts in such a molecule may not 

 occur without our being within a measurable distance of detecting them. 

 For if the number of possible varieties of a protein whose molecular weight is 

 known, and known to be exceptionally small, and which contains the several 

 amino acids in a known proportion, is as great as this, the number that 

 is possible when that proportion may be changed is practically incalculable, 

 each change in proportion being capable of a number of new arrangements 

 that could be calculated, as was done for our hypothetical case. 



But in the living cell where these chains are put together each link 

 must first be fashioned and then forged into the chain- ; unfinished chains 

 in statu vaseendi must exist which our analytical methods can never 

 detect. In such unfinished chains the order presumably in which the 

 amino acids are linked up is observed, but the proportion must be different 

 from that in the finished product ; for in a chain of nearly a hundred links 

 a particular amino acid, cystine, for instance, may occur only once. 



Now it is possible that the analogy of crystal formation may be applied 

 to the reproduction of the characteristic order in which the Unkings 

 occur, and that the parts out of which a new chain is to be formed may be 

 collected and brought into position alongside of the corresponding parts 

 of an existing chain by forces that are similar to those that determine the 

 latticed relations of atoms in a crystal. But something more than this is 

 required to account for the linking up of these links by the loss of water, 

 and still more for the fashioning of the links themselves. In plants all 

 varieties of amino acids come into being as required ; in animals, it is 

 true, some must be supplied ready-made in the medium in which the 

 proteins grow ; but even in animals some of them can be formed from 

 material of a totally different nature. 



Wherever this is the case we have to suppose that it is by selective 

 emphasis of certain otherwise unemphasised but possible arrangements 

 of atoms or groups of atoms, evidence for the occurrence of which under 

 similar conditions in the absence of life is generally not obtainable. Specific 

 catalysed syntheses must co-operate with the forces that merely sort out 

 and place in proper order the assembled parts, and must fashion for them 

 Ihe particular links that they need at each step. Specific catalytic agents 

 playing an important part in cell chemistry are familiar in the enzymes 

 found in digestive secretions and also locked away within the cells 

 themselves. There is much to support the idea that such agents act by 



