432 CHEMICAL DISCOVERY AND INVENTION 



constituent. Changes of this kind now excite very little surprise. 

 Scores of metamorphoses of a similar character are now known, 

 and in the years which have elapsed since Wohler's time hundreds 

 of chemists have been busily at work. It is estimated that about 

 130,000 distinct carbon compounds are now known. These great 

 advances, including the remarkable department of stereo-chemis- 

 try (Chap. XII), which has sprung into existence within the last 

 forty years, are the natural outcome of the pursuit of knowledge 

 for its own sake. Similar advances have been recorded in other 

 branches of science on the recognition of the same principle. 

 But the time has arrived long ago when the systematisation of 

 the vast mass of knowledge acquired concerning the origin, 

 synthesis, and properties of carbon compounds may be turned 

 to account in the endeavour on the part of physiologists to pene- 

 trate some of the mysteries connected with living things. This 

 has become imperatively necessary not only in the practice of 

 medicine, to which the organic chemist has supplied so many 

 now indispensable medicaments, but for the better understanding 

 of the processes which go on in the body, in health as well as in 

 disease. Nor is this knowledge applicable only to the human 

 and animal body. Vegetable physiology brings to the agricul- 

 turist a practical assistance which enables him more successfully 

 to cultivate his land, to understand the application of manures 

 and the rotation of crops, and generally to gather from the soil a 

 larger yield of food stuffs of all kinds. 



But in order that all these applications of chemical knowledge 

 may be accomplished the knowledge itself must be stored up 

 and made accessible. To this end the chemist must study care- 

 fully and record fully the composition and properties both 

 physical and chemical of a very large number of com- 

 pounds. 



It has already been pointed out in the chapter on sugars that 

 not only is the proportion of carbon, hydrogen, and oxygen 

 present in these compounds a matter of importance, but the 

 number of atoms which enter into the molecule and the configura- 

 tion of the molecule, that is the arrangement of the atoms in 

 space, determine the part which these substances play in the 

 vegetable and animal economy. Two sugars may have exactly 

 the same composition and molecular weight and yet the one 

 will have a more decided sweet taste than the other, the one will 

 be resolved into alcohol and carbonic acid by the action of yeast, 



