124 ORIGIN AND NATURE OF LIFE 



chemists and biologists, although it happens 

 to be that one which lies at the very threshold 

 of life. It was opened just fifty years ago 

 by Thomas Graham, who introduced the 

 word colloid because one of the most typical 

 members is gelatine (L. colla, glue). This 

 earliest pioneer with a wonderful clearness 

 of vision recognized the close relationship of 

 colloids to the phenomena of life, and with 

 such a lead it is remarkable that the study 

 was left languishing for nearly forty years. 

 In the last decade it has become a centre of 

 feverish industry with ever-expanding rela- 

 tionships both to modern industries, and to 

 the scientific problems of bio-chemistry and 

 medicine. 



One reason for this neglect undoubtedly 

 lay in the fixed attitude of the chemical 

 theory of the time towards the subject of 

 atomic valencies. It was deemed inconceiv- 

 able that a fully saturated chemical substance, 

 in the atomic sense, could enter afresh into 

 a new round of chemical activities, in which 

 atoms as such did not play a part, but where 

 the whole molecule behaved as an atom. 

 In fact, to the majority of chemists, this is 

 still a heterodox opinion, and they prefer 

 to ascribe such molecular actions to something 

 which they describe as " residual affinity. " 



