1 80 SCIENCE PROGRESS 



not the simplest more advance has been made towards a material 

 explanation of vital phenomena than towards a solution of the 

 simple question why one pair of gases should combine to form a 

 fluid, while another pair combine to form a gas. 



An unanswerable question concerning the elements of natural 

 knowledge is a sharp reminder of our ignorance, and such a 

 reminder is needed to curb the spiritual arrogance which in our 

 time has brought this greatest of all mysteries, the relation of 

 living to non-living matter, to the temples of vulgar credulity, and 

 has prostituted it to the purposes of common charlatans and 

 impostors. 



Since Huxley wrote, our knowledge of the physical basis of 

 life has developed in many directions. The properties of secre- 

 tion and absorption, of contractility and irritability, have been 

 studied in great detail. The classical fields of physiology, the 

 detailed investigation of form, and the anatomy of function have 

 been continuously worked. But the greatest advance has come 

 in the domain of chemical physiology. Ten years ago this was 

 a scientific No Man's Land, despised by the pure chemist and 

 traversed only in a distrustful, amateurish way by the physio- 

 logist. Now that is changed ; on the one hand a race of physio- 

 logists has sprung up who are at the same time expert chemists, 

 on the other one sees a pure chemist, Emil Fischer, of Berlin, 

 bending all the resources of his great laboratory in men and 

 materials to the central chemical problem of living matter, the 

 chemical structure of proteid. 



The few pages at my disposal would not hold even a catalogue 

 raisonnee of the new departures. Therefore it is necessary to 

 select a few problems, and for purposes of contrast I choose not 

 the new but the old, which were agitated half a century ago. 



At the outset, however, it is necessary to state certain ele- 

 mentary facts — that there is a unit of living matter called the cell, 

 which everywhere and in all places has recognisably the same 

 structure ; and that all forms of life are divisible into two 

 divisions : those in which the individual and the cell are coter- 

 minous — the simple-celled forms ; and those more complex and 

 larger types in which the individual is a cell complex — the 

 multicellular forms. The former are probably the more numer- 

 ous, but they escape notice by reason of their small size, which is 

 imposed upon them by a law, wellnigh without exception, which 

 must strike very deeply into the nature of living matter — namely, 



