220 ON VARIABILITY AND ADAPTATION 



in dying, as again in certain of its activities while living, yields 

 proteins. 



So universal, so essential is this association, that clearly 

 the first step to a comprehension of living matter must be 

 gained through a study of proteins and their properties, 

 for the phenomena of living are clearly bound up with the 

 processes of association and dissociation of bodies of this par- 

 ticular order. Over more than fifty years the physiological 

 chemists have been working at the problem of the constitution 

 of these proteins. At first the problem seemed hopeless. It 

 was found that they were formed of carbon, hydrogen, oxygen, 

 nitrogen, sulphur, but the formula of constitution was some- 

 thing appalling. Common salt, NaCl, for example, consists 

 of one atom of chlorine (CI) joined to one atom of sodium (Na). 

 But in these proteins the amount of sulphur to be obtained is so 

 minute compared with the amount of the other constituents that 

 obviously the molecules are of enormous size. Take, for example, 

 one of the proteins which, since it can be obtained in a crystalline 

 form, must be regarded as among the less complex, namely 

 haemoglobin, the protein which gives the red colour to the cor- 

 puscles of the blood. Its molecular composition is somewhere 

 in the neighbourhood of 



The molecular weight of water, formed of two parts of hydrogen 

 to one of oxygen, is 16 ; the average molecular weight of the 

 proteins has been estimated at 15,000, or, otherwise, this molecule 

 is about 1000 times as weighty as is the molecule of water. I 

 say in the neighbourhood of these figures, for no two samples 

 yield identically the same results. It seemed impossible to 

 think of building up experimentally such hugely complex bodies. 

 Next it was found that these molecules are, as I may express 

 it, conglomerates. Haemoglobin, for example, can be spb't up 

 into an iron-containing protein, haematin, and an iron-free 

 globulin ; and in the 'seventies and 'eighties a material advance 

 was made in the study of the products of splitting up the mole- 

 cules by the action of acids and of the digestive ferments. The 

 peptones and albumoses so obtained were found to be less 

 complex. In the 'nineties Kossel discovered a group of proteins, 



