78 ANIMAL CHEMISTRY LECTURE IV. 



external 4> rce ' Speaking of the progress of natural science, 

 Mr. Mill has very pertinently observed that for a long time 

 ' fictitious entities continued to be imagined as means of account- 

 ing for the more mysterious phenomena; above all, in phy- 

 siology f where under great varieties of phrase, mysterious forces 

 and principles were the explanation, or substitute for explanation, 

 of the phenomena of organised beings.' 



(83.) Seeing, then, that the enormous number and variety of 

 animal and vegetable compounds are produced out of carbonic 

 acid, water, and ammonia, not by any peculiar vital force, but 

 merely by the light and heat force of the sun acting through 

 organic machinery, the question naturally arises whether the 

 chemist may not effect in his laboratory-machinery a similar 

 intercombination of deoxidised carbonic acid and water, either by 

 a direct application of sun-force, or, indirectly, by the aid of 

 those terrestrial transformations of sun-force which are so abun- 

 dantly at his disposal. This question, decided absolutely* in 

 the negative BO long as the fiction of vital force tyrannised 

 over men's minds, has of late years received a rapid suc- 

 cession of brilliant affirmative replies. Already hundreds of 

 vegetable compounds heretofore produced only in living or- 

 ganisms, and, as was supposed, put together and held together 

 by vital force, have been formed by the chemist in his laboratory 

 out of carbonic acid, water, and ammonia, or, in other words, 

 out of charcoal, hydrogen, oxygen, and nitrogen. That a still 

 greater number of compounds have not been so formed is due 

 more to a deficiency of knowledge than of power ; for as our 

 acquaintance with the constitution of bodies, and with synthetic 

 processes, is daily advancing, so is the unlimited constructive 

 power of chemical art becoming daily more and more apparent. 



(84.) Before proceeding, however, to exemplify this power of 

 forming organic compounds artificially, I will first make one or 

 two further remarks upon the order of their natural production. 

 At present we are unable to trace the series of changes, undergone 

 by carbonic acid and water, which result in the formation of tar- 

 taric acid, or sugar, or fat, or other complex vegetable product. 



