PHYSIOLOGICAL 337 



and inanimate? An illustration will answer. The physiologist is 

 interested in pigments like haemoglobin and chlorophyll, for their 

 utility to the organism is fundamental. But there are many other 

 pigments that have not this directly useful role, though they are 

 secondarily of great value in concealing the animal, or advertising 

 it, or dressing it in bright attire useful in courtship. These secondary 

 utilities are often demonstrable, and it is reasonable to suppose that 

 the coloration might be gradually elaborated by Natural Selection. 

 Yet the difficulty has been to explain how the coloured material is 

 there at all; and it is here that the biochemist comes in, by telling 

 us the chemical nature and the probable derivation of the pigments 

 in question. Thus he tells us that the green biliverdin of the Verte- 

 brate's bile and of some tissues in Invertebrates may be regarded as 

 a degradation product of haemoglobin. Similarly, the dark melanin 

 pigments of dark hair, feathers, skin, and so forth, are derivable 

 from some of the abundant amino-acids (like tyrosine) into which 

 proteins break up. The ruddy lipochromes — so widely distributed, 

 as from the Norway lobster to the wattle of the red grouse — are 

 traceable back to leaf pigments, which may be taken into the animal 

 directly or indirectly as part of the food. The point should be clear. 

 Given a natural supply of certain pigments which can readily be 

 accounted for in the chemical routine of the body, we are in a better 

 position to understand their secondary utilisation. They are there 

 for the using, so to speak — for the using if needs be — in the everyday 

 life of the creature, whether as protection, or warning, or decoration. 



Can chemistry also be of service in the working out of a theory 

 of organic evolution ? The question is almost answered in the asking; 

 for organisms evolve in a chemical and physical environment with 

 which they are in intimate and subtle relations. A slight difference 

 in the nutrition and environment of two apparently identical larvae 

 (of the green worm BonelUa), and one becomes a large independent 

 female, the other a pigmy parasitic male. That is for the individual, 

 but the same kind of influence must also have affected the race. 

 Hereditary nature and environing and functional nurture work into 

 one another's hands; both are components of the resultant — 

 developmental and evolutionary alike. 



But if we consider such a fine piece of work as Gautier's analysis 

 of the serial chemical differences between different varieties of 

 grapes, or the memoir of Reichert and Brown on the differences in 

 the haemoglobin of even nearly related mammals, we get a glimpse 

 of another important and promiseful contribution, for there is a 

 chemical basis for species. All flesh is not the same flesh ; but there 

 is one flesh of man and another of fishes. Every type has its own 

 protein ; there is a chemical accompaniment of individuality. 



What will be left when the chemistry and the physics of the 

 hving body have continued their work for several centuries? A 



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