8 INTRODUCTION. 



or inorganic, and we have considered the means by which these bodies 

 may be separated: we, therefore, here leave the inorganic world (the 

 domain of physics, chemistry, mineralog} r , etc.), to confine our studies 

 to the animal kingdom. But here, from the fact that there was great 

 difficulty in separating the lower forms of animal from vegetable life, it 

 must be recognized that animals and plants possess many vital functions 

 in common ; and as the simplest expression of these functions must be in 

 the simplest organisms, the study of those functions may best commence 

 in the simple, uncellular organisms, whether animal or vegetable. 

 General physiology will thus deal with the Animal Cell : its form, origin, 

 modifications, constitution, and the various chemical and physical proc- 

 esses concerned in its nutrition, growth, development and reproduction. 



It will, then, be shown that the higher animals are mere associations 

 of such simple organisms, in which the modification in the characters 

 of the various constituent cells leads to a division of labor. In other 

 words, development of tissues leads to a specialization of function, and 

 Special Physiology will deal with the study of the development of func- 

 tion, especially as seen in our domestic animals. The functions of animals 

 are divided into the Vegetative Functions, the Animal Functions, or 

 the functions of relation, and the Reproductive Functions. 



The Yegetative Functions include everything which relates to the 

 nutrition of the animal in its widest sense. As the blood in higher 

 animals is the organ of nutrition, under this head are included (1st) 

 the additions to the blood, therefore, the description and modes of 

 prehension of Food ; Digestion, or the preparation of food for absorption ; 

 and Absorption, or the means by which nutritive and other matters enter 

 the blood. The Blood will, then, be considered as a tissue of nutrition 

 <or as a carrier to and from the various organs of the body by means of 

 its Circulation. As a boundary between the additions and (2d) the losses 

 to the blood Respiration will demand attention, while under the latter 

 head come the functions of Secretion and Excretion. The means by 

 which the identit}^ of the individual is preserved concludes the subject 

 of Nutrition and deals with the nutritive value of different foods and 

 their combinations, the adaptment of foods to the different demands on 

 the animal economy, and the subject of Animal Heat. The Animal Func- 

 tions, or those by which the body is brought into relation with the 

 external world by means of sensation, power of movement, consciousness, 

 and volition, include the study of the Muscular and Nervous Systems, 

 while finally the Reproductive Functions lead to the preservation of the 

 species, and include the subjects of Generation and Development, or 

 Embryology. 



