PHYSIOLOGICAL 333 



the conversion of "fixed air" or carbon dioxide into "dephlogisti- 

 cated air" or oxygen. Let our thoughts run on for a century and a 

 half or so; and we now read that chlorophyll is a complex of four 

 pigments; that the most useful rays are the reddish rays; that the 

 light is probably transformed to electricity, which reduces the 

 carbonic acid to formic acid (CH^Oa) and later to formaldehyde 

 (CH^O), a molecule of oxygen being set free as a by-product — a 

 precious by-product by which we live. Then comes the main product, 

 glucose, and the end-products are proteins. Without chemistry it is 

 all "joukery-pawkery". But let our thoughts go once more to 

 Prof. Baly's laboratory, in Liverpool, where the students can 

 sweeten their tea with synthetic sugar built up by the light of a 

 mercury vapour lamp shining through a vessel containing carbon- 

 dioxide and water. Thus the work of the green leaf is mimicked in 

 the test-tube by the production of formaldehyde, and later on of 

 sugar, from carbon dioxide and water. Let our thoughts go on still 

 farther, to the very interesting chemical analogy between chlorophyll 

 and haemoglobin ; but this takes us into deep waters ! 



Chemistry and physics have joined hands so firmly in recent 

 years, that demarcation of the fields of inquiry is practically 

 impossible; and therefore we need not apologise for taking as our 

 next illustration the study of colloids. It is not too much to say that 

 our view of the activities that go on in the living cell has been 

 almost entirely changed by a knowledge of the properties of matter 

 in a colloid state ; and we may date the beginning of this knowledge 

 from Thomas Graham (1861). Living matter is in a colloidal state; 

 that is to say, there are countless ultra-microscopic particles and 

 droplets suspended or dispersed in a more or less liquid medium. 

 The boundary surfaces of contact between the countless particles or 

 droplets and the medium are enormous in proportion to the total 

 mass, and on these surfaces there is room for a multitude of chemical 

 and physical actions to take place. This fundamental fact helps us 

 greatly towards an understanding of the prodigious effectiveness of 

 the living cell. 



We have given two instances of foundation-stones (laid by 

 Lavoisier and Liebig), two instances of the great initiatives (on the 

 part of Wohler and Pasteur), two examples of fundamental con- 

 tributions still being added to (the study of photosynthesis and 

 colloids); and now we must be content to take two examples of 

 distinctively modem contributions. We would refer first to the 

 discovery of glutathione by Gowland Hopkins in 1921. This gluta- 

 thione is an organic substance, falling naturally into three parts, 

 all of which are amino-acids — glycine, glutamic acid and cystein 

 — and it will, of course, be kept in mind that the most essential 

 components of living matter, the proteins, are chains of amino- 

 acids. The most important property of glutathione is that under 



