VI PREFACE TO TEE FIRST EDITION. 



cussed : this was deliberately done as the result of an experi- 

 ence in teaching Physiology which now extends over more 

 than ten years. It would have been comparatively easy to 

 slip over things still uncertain and subjects as yet unin- 

 vestigated, and to represent our knowledge of the workings 

 of the animal body as neatly rounded off at all its contours 

 and complete in all its details totus, teres, et rotimdus. 

 But by so doing no adequate idea of the present state of 

 physiological science would have been conveyed; in many 

 directions it is much farther travelled and more completely 

 known than in others; and, as ever, exactly the most inter- 

 esting points are those which lie on the boundary between 

 what we know and what we hope to know. In gross Anatomy 

 there are now but few points calling for a suspension of judg- 

 ment; with respect to Microscopic Anatomy there are more; 

 but a treatise on Physiology which would pass by, unmen- 

 tioned, all things not known but sought, would convey an 

 utterly unfaithful and untrue idea. Physiology has not fin- 

 ished its course. It is not cut and dried, and ready to be 

 laid aside for reference like a specimen in an Herbarium, but 

 is comparable rather to a living, growing plant, with some 

 stout and useful branches well raised into the light, others 

 but part grown, and many still represented by unfolded buds. 

 To the teacher, moreover, no pupil is more discouraging than 

 the one who thinks there is nothing to learn; and the boy 

 who has " finished " Latin and " done " Geometry finds some- 

 times his counterpart in the lad who has " gone through " 

 Physiology. For this unfortunate state of mind many Text- 

 books are, I believe, much to blame : difficulties are too often 

 ignored, or opening vistas of knowledge resolutely kept out of 

 view: the forbidden regions may be, it is true, too rough for 

 the young student to be guided through, or as yet pathless 

 for the pioneers of thought; but the opportunity to arouse 

 the receptive mental attitude apt to be produced by the rec- 

 ognition of the fact that much more still remains to be learned 

 to excite the exercise of the reasoning faculties upon dis- 

 puted matters and, in some of the better minds, to arouse 

 the longing to assist in adding to knowledge, is an inesti- 

 mable advantage, not to be lightly thrown aside through the 

 desire to make an elegantly symmetrical book. While I 

 trust, therefore, that this volume contains all the more impor- 

 tant facts at present known about the working of our Bodies, 



