190 THE AMERICAN NATURALIST. =- (VOL; XXXIII. . 
And, finally, as a crowning glory of the seventeenth century, 
we must not forget the inauguration in it of the science of 
embryology, with which the name of Harvey must also be 
associated, his predecessor in the study being his teacher, 
Fabricius ab Aquapendente. : 
But it is merely the beginnings of these various adjuncts to 
anatomy that we find at this period. At this time, and indeed 
until much later, anatomy was regarded simply as a medical 
study, and investigation in it was conducted for a distinctly 
practical end. On account of its relations to medicine it came 
under the influence of the medical theories which prevailed at 
the time, and these theories, frequently changing, at one time 
stimulated observation and at another retarded it. Anatomy, 
instead of flourishing under a theory of its own, was over- 
shadowed by, or received but reflected lustre from medical 
theories, and it is of interest on this account to consider these 
latter briefly. 
If I were asked to characterize in a few words these theories, 
I would say that they belong to two distinct classes, those of 
the one class being based upon a dualistic conception of the 
structure of the body, while those of the other might be termed 
monistic. Those of the one class seem to have served as 
stimuli to those of the other, and the history of the theory of 
medicine from the sixteenth to the beginning of the nineteenth 
century has been a history of an almost regular alternation of 
dualistic and monistic hypotheses. As pertaining to the dual- 
istic group, the sixteenth century doctrines of Paracelsus may 
be mentioned, according to which the physiological and patho- 
logical processes of the body were the result of a controlling 
spirit, termed the Archeus, and this view was also maintained 
with slight modifications by Van Helmont in the beginning of 
the seventeenth century, he, too, recognizing a dominant 
Archeus to whom were subordinate other Arche? insiti, disease 
being due to “the passions and perturbations of the Archeus,” 
and the treatment of the physician an attempt to modify the 
ideas or emotions of this evs. 
Naturally there was ere long a reaction from such a fantastic 
hypothesis, and we find in the seventeenth century two monistic 
