130 THE PATH OF SCIENCE 



the sugars and synthesized many of them, identifying and, 

 in many cases, preparing the stereoisomeric forms. The dif- 

 ficulties produced by fermentation in this work turned 

 Fischer's attention to the chemical ferments and enzymes, 

 in regard to which he and his coworker, E. Abderhalden, laid 

 the foundations of our present knowledge. 



From the sugars and ferments Fischer transferred his at- 

 tention to the proteins. He succeeded in breaking down 

 these complex products of vital metabolism into amino acids 

 and other nitrogenous compounds, solving their constitution 

 and synthesizing them. He was thus able to prepare in the 

 laboratory polypeptides analogous to the natural proteins. 



Other fields of the chemical study of naturally occurring 

 substances relate to the plant alkaloids, which are of great 

 pharmaceutical interest, and to the coloring matters of plants. 

 Perhaps the most striking examples of this field of chemistry 

 are the recent determinations of the structure of the vitamins 

 and the hormones derived from the ductless glands. The 

 industrial production of synthetic vitamin C (ascorbic acid) 

 and especially of vitamin Bi (thiamin) provides an adequate 

 supply of these necessary materials. 



The properties of the compounds of carbon and their pro- 

 duction by synthesis are the field of organic chemistry. On 

 the other hand, the study of chemical reactions and of the 

 equilibria produced in those reactions is the field of physical 

 chemistry. 



It had long been known that the progress of a chemical 

 reaction is influenced by the amounts of the reacting sub- 

 stances, but it was not until 1850 that the progiess of a 

 reaction was measured and the results expressed as a mathe- 

 matical equation. This was done by L. Wilhelmy at Heidel- 

 berg, who showed that when cane sugar was inverted by acids, 

 a reaction which can be followed with the polariscope, the 

 amount of cane sugar inverted in a unit time is proportional 

 to the amount of sugar present. Just at that time, the atten- 

 tion of chemists was largely directed to the discussion con- 

 cerning the structure of organic compounds, and it was twelve 



