524 POPULAR SCIENCE MONTHLY 



of preformation was attracting wide interest. This had stimulated 

 Caspar Friedrick Wolff to the production of his Theoria Generationis, 

 which was unfortunately held in the dark by the opposition of Haller 

 who could not accept the principles which led, at a somewhat later 

 date, to the conception of Epigenesis. The theory of irritability was 

 also a bone of contention, and though it was materially furthered 

 toward the true conception by Haller's own researches, these last, 

 unfortunately, served also to further a doctrine which thoroughly 

 permeated and confused the development of all physiology down to 

 the middle of the nineteenth century. This was due chiefly to the 

 following fact: That the seeming impossibility of explaining the phe- 

 nomena of irritability led to the welcoming of the theory of vitalism, 

 or vital force, which asserted a distinct dualism between living and 

 lifeless nature. The vitalists at this time (and nearly all the natural 

 scientists, except perhaps Eudolphi at Berlin, were vitalists in a greater 

 or lesser degree) were discarding the mechanical and chemical expla- 

 nation of life phenomena, and were introducing such mysterious and 

 inscrutable explanatory principles as la force hypermecanique and the 

 nisus formativus. In this acute and exhaustive manner were explained 

 even the most complex of vital phenomena. 



Toward the end of the eighteenth century, however, some twenty 

 years before the birth of Muller, a new note was being sounded from 

 the ranks of German scientists, especially from Reil, whom we may 

 well call the censor of German vitalism. In his work " Ueber die 

 Seelenskraft," he was forcing upon unwilling hearers not only the con- 

 ception that the life phenomena of living organisms are regulated by 

 chemico-physical laws, but that there were higher principles in control 

 which were present only in living matter. The few adherents to the 

 chemico-physical hypothesis were, during the last years of the eight- 

 eenth century, receiving fundamental support from such men as Bitter, 

 Galvani and Humboldt. Through the work of these men the notion 

 was becoming popular that the galvanic current was the cause of all 

 vital phenomena. 



Among the chemical and physical discoveries of this time we can 

 mention the advance of vegetable physiology through Ingenhaus 

 (1730-99), who developed the theory of the consumption of carbon 

 dioxide by plants; the discovery of oxygen by Priestley (1733-1804) 

 and Lavoisier (1743-94), and the further discovery in this line by 

 Girtanner, who showed that the venous blood is aerated in the lungs. 

 Thus the existence of the mystical " pneuma," which had clung with a 

 peculiar persistence to centuries of physiological thought, had now be- 

 come a reality. The anatomical researches of this period were char- 

 acterized by one discovery in particular, announced by Charles Bell 

 in 1810; that is, the fundamental law of specific nerve physiology, to 

 be later experimentally proved by Johannes Muller. In microscopy, 



