142 



SCIENCE PROGRESS. 



H 2 COH 

 HCOH 



, from which only the non- 



can be derived. (Each of 



must have the formula 



HOCH 



OCH 



HC0 2 H 



• , . , HCOH 

 symmetrical acid 



H O CH 

 C0 2 H 

 these types of tetrose corresponds with two isomers, right 

 and left.) Through the experimental work of Fischer and 

 Kiliani it has even been found possible to assign its proper 

 formula to each of the seven known glucoses, CH 2 OH 

 (CHOH) 4 COH, the guiding-thread being always the con- 

 tion between inactivity and symmetry of formula among the 

 derivatives, and between activity and lack of symmetry. 



The configuration of the unsaturated compounds CR'R" 

 CR'"R 1V is represented by placing the tetrahedral models 

 edge to edge (see the solid formulae for fumaric and maleic 



▼v ^W 



COoH 



Smm 



^2*& 



Plate. II. 



