226 NATURE AND LIFE. 
the manifest symptoms arising from disorder of the organs, 
to distinguish the parts affected, and to decide on the kind 
of change they have undergone; it is indispensable, besides, 
to investigate the alterations occurring in the direct com- 
position of the secretions and excretions, as well as the 
passages and modes by which the active substances are 
eliminated; and, moreover, to measure the variations of 
temperature, pressure, muscular energy, etc., by which the 
therapeutic acticn becomes evident. To carry out success- 
fully so complicated an examination, we use the common 
implements of vivisection, recording contrivances, most of 
which were devised by Marey, chemical reacting agents, 
microscopes, spectroscopes, and polarizers. In a word, all 
the sciences yield their tribute to the physiologist who 
seeks in his turn to furnish the physician with therapeutic 
precepts that may be confidently applied. 
Such are, in respect to physiology, the just hopes of 
therapeutics. It may fairly indulge no less promising ones 
with regard to chemistry. The latter, which has already 
rendered so many and so great services to the healing art, 
will render it the last and the most desirable of all, by the 
artificial creation of those active principles which we are 
as yet still compelled to extract from vegetables. The 
preparation of the alkaloids by the aid of plants is so te- 
dious and costly, and may be impeded in certain contin- 
gencies in a way so injurious to the interests of public 
health, that chemists should exert themselves to make 
those operations of a rude art unnecessary for the future. 
The knowledge of the inner structure of molecules is com- 
plete enough, the power of methods of synthesis is perfect 
enough, to allow such an attempt to be undertaken without 
rashness. In the vessels of a laboratory, vegetable acids, 
essences, and fats, are reproduced complete; pungent per- 
fumes and brilliant colors are prepared from them by deli- 
cate chemical reactions ; why might not chemists discover 

