SEVENTEENTH AND EIGHTEENTH CENTURIES 183 

 Those of Stahl's contemporaries who adopted his ideas were at any rate 

 not compelled to associate themselves with the peculiar theories referred to 

 above. His criticism of that age's mechanistic conception of life is indeed 

 often of such penetrating keenness that it must have proved attractive to 

 those who sought to probe the contemporary controversial problems in that 

 sphere. Especially does he inveigh against the theories of these "vital 

 spirits" on which his opponents' explanations of the phenomena of life 

 rested and which they could not possibly do without. Compared with these 

 theories his soul-theory was at least simple and easy to comprehend; it cleared 

 up satisfactorily enough the question of the relation of the psychical phe- 

 nomena to the material, a problem on which all previous attempts to explain 

 mechanically the phenomena of life came to grief. Stahl also had a sharp 

 eye for other weaknesses in the contemporary explanations of life and demon- 

 strated their inanity, as, for instance, the pan-sperma theories that were so 

 common at the time. Besides his above-mentioned keen analysis of the con- 

 trasts between living and inorganic natural objects, which is only briefly 

 summarized here, these critical contributions relating to the controversial 

 biological questions of his age constitute Stahl's great service to science. 

 This is, it is true, counterbalanced by his vague, yet subtle, natural philosophy, 

 which has also been but briefly recounted here, and the understanding of 

 which is rendered all the more difficult by a very obscure and badly arranged 

 method of presentation. He gained many followers among his contempora- 

 ries; several of his own pupils gave practical demonstrations of the dangers of 

 regarding the soul as an instrumental component in the functions of the body 

 and the treatment of disease by indulging in extravagant speculations along 

 mystical and theosophical lines. The valuable parts of his theories were 

 most strictly adhered to and most faithfully developed at the University of 

 Montpellier, where an entire school of physicians embraced his ideas. Among 

 his opponents may be especially mentioned, besides his old friend Hoffmann, 

 Leibniz, who in a contentious pamphlet sharply inveighed against his con- 

 tempt of anatomy, chemistry, and other exact methods of research, and, from 

 the standpoint of his own monad theory, rejected Stahl's theories of the soul 

 and motion as being separate from the material part of living beings and as 

 factors operating independently thereof. The influence that Stahl had on the 

 development of biology in later times may at first glance seem small; in- 

 directly, however, he has certainly been of greater significance than many of 

 those who are more frequently quoted. Among those who have openly 

 acknowledged their indebtedness to him may be mentioned such a compara- 

 tively well-known scientist as the embryologist Caspar Friedrich Wolff. 



The man who, of the medical and biological theorists of that time, 

 undoubtedly enjoyed the highest reputation among his contemporaries was, 

 however, Hermann Boerhaave. He was born in 1668, the son of a country 



