18 TRANSACTIONS .LIVERPOOL BIOLOGICAL SOCIETY. 



is in the iris some radially disposed structure which by its 

 contraction dilates the pupil and causes this second set of 

 folds. Why then did the older physiologists give it up and 

 even consider themselves wrong? Because they had 

 deduced a structure from the function and assumed that 

 this radial structure must be a conspicuous muscle. There 

 is no conspicuous radial muscle, but a more careful exam- 

 ination by Heese has shown isolated radial fibres, though 

 whether muscular or not we do not yet know. 



Function here has guided finally after many failures to 

 structure. Mistakes may occur, but the advantage of 

 inferring the structure from the function is often quite as 

 great as the reverse inference. To it we owe the dis- 

 covery of structural changes underlying the chemical 

 processes of living cells. 



Fifth class of instances; changes in Structure discovered 

 to underlie changes in Chemical Activity. 



For years microscopic investigation in conjunction with 

 Anatomy was the sole guide in the endeavour to find such 

 changes, but a time came when this investigation unaided 

 by a knowledge of the function seemed to be insufficient. 

 To make this clear, take the activity of secreting cells. 



The salivary glands, pancreas, stomach, liver, etc., each 

 secretes its own special digestive fluid. The juices, and the 

 antecedents of their constituents, are evidently manu- 

 factured in the cells of each special gland, and such cells, 

 when examined microscopically, showed characteristics 

 which distinguished them from others. What, however, 

 are the structural features in the cell which are associated 

 specifically with the manufacture ? To this question 

 the older Histology could give no satisfactory reply ; it 

 seemed almost beyond the limits of histological manipu- 

 lative possibility to even give us a lead. Then the subject 



