I.— PHYSIOLOGY. 211 



modifying the chaotic, indeterminate, kinetic agitation of certain kinds 

 of molecules in their immediate neighbourhood in such a way that the 

 relative positions in space of groups capable of reacting with one another 

 tend to become those in which reaction is likely to occur and to occur in 

 conformity with a certain pattern. The peculiar thing about the chemistry 

 of living matter is not that the reactions that are characteristic in it are 

 novel, but that in the rough and tumble of ordinary liquid systems their 

 occurrence is almost infinitely improbable. Where there is life, circum- 

 stances exist which make them the rule. Anyone conversant with work 

 in animal metabolism can supply many illustrations ; for instance, it has 

 been shown that in a simple solution of the amino acid, alanine traces of 

 methyl glyoxal occur ; in the animal body there is reason for thinking 

 the reaction may become practically quantitative. Forces which deter- 

 mine the relative positions of adjacent foreign molecules and so affect 

 their behaviour are something to which there is no analogy in the growth 

 of crystals in a saturated solution. 



Moreover, if the forces that determine the reproduction of a certain 

 order in the arrangement of the parts of a protein are similar to those 

 that determine the lattice pattern of a crystal, the crystals with which 

 the comparison is made are solid, and life is manifested only in liquid 

 aqueous systems. The analogy should rather be with the formation of 

 licjiiid crystals, a phenomenon that is itself as yet too urifamiliar to shed 

 common light on the obscurity of spontaneous regeneration. The ordered 

 disposition of the ultimate components of protoplasmic systems is such 

 as to leave play, generally but little checked, for the fluid properties of 

 water, and in some modified degree too of molecules and ions dissolved 

 in water. Even a solid jelly may include within its protein framework a 

 hundred times its weight of water in which diffusion is free to take place 

 almost as if the framework were not there, and protoplasm, with 

 commonly twenty times as much protein in it as this, more often resembles 

 a fluid of varying viscosity than a solid gel, which means that the great 

 protein chains float and drift in the whirlpool of kinetic agitation, 

 observing, it may be, so far as is possible, certain unstable relations to 

 their kind, but with no rigid fixity. It is commonly felt that the behaviour 

 of iinicellular organisms makes the hypothesis necessary that there is an 

 insoluble surface layer that keeps the watery contents of the cell from 

 dispersing in the water that surrounds it. Much experimentation, and 

 no lack of speculation, has not made clear what the nature and structure 

 of this limiting layer is. It may be that the flexible cohesion at many 

 alternative points between clinging floating chains of amino acids, the 

 innermost of which are made fast to the nucleus, may go some way to 

 maintain the identity of the cell and prevent its contents from scattering. 



But in the chemical make-up of protoplasm, proteins, the most abundant 

 component, are not the only ones that are necessary. Pre-eminent among 

 the others are the nucleic acids. When we consider what has been learnt 

 of the behaviour and of the chemical composition of the nuclear chromo- 

 somes, and that according to Steudel's reckoning the nucleic acids form 

 '40 per cent, of the solid components of these chromosomes, into which 

 are packed from the beginning all that pre-ordains, if not our fate and 

 fortunes, at least our bodily characteristics, down to the colour of our 



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