304 THE HISTORY OF BIOLOGY 



life; on the subject of vitalism, as maintained by Stahl's successors, he holds 

 that, while it is true that a number of phenomena exist only in living crea- 

 tures, nothing is gained by referring to the soul as their cause; they should 

 rather be regarded as physical phenomena and studied through observation 

 and experiment, but not ascribed to a principle "whereby thought retires 

 in the belief that everything is done, when in reality everything remains 

 to be done." This criticism he extends to several current hypotheses; thus, 

 he rejects the assumption of a fluid controlling the impulses in the nervous 

 system, for by this particularization of a little-known function a number of 

 illusions have been created, while such an expression as "nervous force" 

 would be far more applicable to the actual knowledge we possess of the 

 phenomenon. Similarly he criticizes the theory current at the time, which 

 originated in Buffon, that the different parts of the embryo are derived from 

 corresponding parts in the parents — a theory that even Darwin afterwards 

 entertained. In disproof of it Vicq d'Azyr adduces the fact that two parents 

 who have lost one and the same part of the body nevertheless produce normal 

 offspring. In this point he has thus foreshadowed views that are expressed 

 by modern students of heredity. 



As his teacher in scientific criticism Vicq d'Azyr mentions the philoso- 

 pher of enlightenment Condillac (1715-80), who enjoyed a great reputation 

 in his time and who made a special study of the relation of sense-perception 

 to the consciousness — he asserts that the consciousness is composed of what 

 the sense-impressions communicate from the outside world — and in con- 

 nexion therewith he maintained that in science words should exactly convey 

 the ideas they are intended to denote. By a careful study of his writings 

 Vicq d'Azyr undoubtedly learnt to realize the necessity for clear ideas and 

 unambiguous terms in natural science as much as in anything else. 



Vicq d' Ax,yr s comparative anatomy 

 VicQ d'Azyr's influence has been felt not only on account of this criticism, 

 valuable as it is, but in a still greater degree as a result of his studies in 

 comparative anatomy, which were unfortunately fragmentary; the prin- 

 ciples on which he worked, however, he summarized in the form of a pro- 

 gram for a course of lectures in anatomy and physiology. The subject is first 

 of all divided up according to the nine life -functions referred to above. Under 

 the heading "ossification" he first deals in descriptive form with the bone- 

 structure and its articulation and forms of connexion, then by way of com- 

 parison the individual bones in different animal forms, and further a number 

 of physiological experiments in connexion with the growth and regeneration 

 of bones, and finally he gives an account of the chemical composition of 

 osseous tissue. Under the heading "irritability" is discussed the muscular 

 system, first descriptively, then comparatively, as regards both conformation 

 and finer structure, the vascular and nervous ramifications, and, finally, ex- 



