vi PREFACE. In arranging the volume now offered to American readers, from the materials furnished in Müller’’s Elements of Physiology, the editor has endeavoured to procure reduction in size of this latter, without any ab¬ straction of its vitality and mind. With this view he has omitted, for the most part, mere disquisitions, many details of experiments, matters of physics and natural philosophy, including mechanics under the head of locomotion, acoustics and the theories of music under voice and hear¬ ing, and of optics under vision,—much of the minutiae of comparative physiology, and metaphysics or metaphysico-physiology. But, while ex¬ cluding details on collateral topics, the editor has been particularly careful to preserve physiology proper, which, resting on the basis of histogeny and general anatomy, derives important aid from organic chemistry and microscopical observations, and, in its turn, serves to illustrate hygiene, pathology and therapeutics. Thus aided and thus applied, in the man¬ ner exhibited by Müller himself, physiology will invite the attention of the student in these pages. It will soon be discovered that, although this volume is an abridgement of the large work of Müller, it may rightfully claim to be considered a complete system of physiology, exceeding in copiousness and com¬ prehensive details, any other work on the same subject, which has yet emanated from the London press. Ample apology for the exclusion of topics merely collateral, which are taught and explained in separate and appropriate works, is fur¬ nished by the author himself, as indeed by other physiologists of dis¬ tinction, in his purposely omitting to describe the details of the struc¬ ture of each organ. He very properly refers the student for these matters to books of special anatomy. With still greater propriety should a similar reference be made when questions on the theories of light and colours, and of acoustics, &c. are under notice. If a mode¬ rate acquaintance with chemistry is supposed to be possessed by the student of Physiology, ought wè not à fortiori to presume that he is not ignorant of, or at least can soon acquire, a sufficient knowledge of optics, acoustics and mechanics, to follow his author and to under¬ stand the allusions to various points included in these branches of science? The reduction has not been after a uniform scale or rule of definite pro¬ portion. In some parts of the ‘Elements,’ comparatively little abbrevia¬ tion has been attempted;-—as in the prolegomena of general physiology, which is a carefully condensed summary of the subjects embraced under the general head, and does not admit, without obscurity, of any material curtailment. So, likewise, in the case of the functions of organic life, those of assimilation, nutrition and decomposition, much of the