l8o THE HISTORY OF BIOLOGY 



This theory rendered possible a uniform conception of a number of processes 

 of conversion in inorganic nature; it constituted a working hypothesis 

 which had a great influence upon the science of chemistry in succeeding ages 

 and made the eighteenth century a period of brilliant achievement in chemi- 

 cal history; names such as Priestley, Bergman, Scheele, bear witness to the 

 progress made in chemistry when the phlogiston theory was dominant; and 

 when eventually Lavoisier, by introducing the weighing method, proved 

 that the theory was untenable and substituted the idea of oxidation for cal- 

 cination, the new theory could be applied directly to the discovery that had 

 been made when the old theory prevailed. Were it only for the advance he 

 thus brought about in chemistry alone, Stahl would deserve a place in the 

 history of biology, which has been so essentially dependent upon the prog- 

 ress of chemistry, and indeed will always be so. 



StahVs medical theory 

 What constitutes Stahl's principal claim to be mentioned as a biologist, 

 however, is the theory of life which he expounds in his great work Tbeoria 

 rnedica vera, in which he seeks to formulate a general theory of the human 

 body and its functions, both in its normal state and in sickness. He himself 

 has declared, and it has been repeated after him, that his chemical theories 

 exercised no influence upon his ideas on the subject. This is true in so far as 

 he does not — like his predecessors amongst medical chemists, Paracelsus, 

 van Helmont, and others — base his entire conception of the human body 

 upon speculation as to its chemical composition, but, on the other hand, the 

 essential part of his work gives ample proof that chemistry is the science on 

 which he bases his ideas. Above all, he is no anatomist; he scorns the result 

 of ordinary macroscopical anatomy and he can hardly find words to express 

 his contempt for Leeuwenhoek's and de Graaf's microscopical investigation 

 of the sexual products; he likewise strongly contemns the discovery of the 

 capillary system, the existence of which he simply denies. On the other hand, 

 he displays a very keen interest in the "mixing {nnxtio)" of the body and its 

 parts — that is, their chemical composition — and he believes that a true 

 conception of the phenomena of life should be based on the knowledge of 

 this ' 'mixtio.' ' Indeed, it is in this direction that he has performed his greatest 

 services to biology. 



The first chapter of Stahl's principal work, mentioned above, is entitled 

 "An Examination of the Difi^erence between Mechanism and Organism." 

 This title might well hold good for the whole of Stahl's literary work 

 on general science; the contrast mechanism--organism is to him the main 

 point in both biology and medical science; he discusses it from every con- 

 ceivable point of view, and in support of his views thereon cites a number 

 of arguments, both good and bad. The main argument, which he repeats 

 again and again in proof of his theory, is that organism is something funda- 



