30 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



isms existing in each animal. In the higher animals, particularly, the com- 

 binations of various tissues and organs into complex mechanisms such as 

 those ol* respiration, circulation, digestion, or vision, differ more or less in 

 each group and to a minor extent in each individual of any one species. It 

 follows, therefore, that each animal has a special physiology of its own, and 

 in this sense we may speak of a special human physiology. It need 

 scarcely be -aid that the special physiology of man is very imperfectly known. 

 Books like the present one, which profess to neat of human physiology, con- 

 tain in reality a large amount of general and special physiology that has 

 been derived from the study of lower animal forms upon which exact experi- 

 mentation is possible. Most of our fundamental knowledge of the physiology 

 of the heart and of muscles and nerves has been derived from experiments 

 upon frogs and similar animals, and much of our information concerning the 

 mechanisms of circulation, digestion, etc. has been obtained from a study of 

 other mammalian forms. We transfer this knowledge to the human being, and 

 in general without serious error, since the connection between man and related 

 mammalia is as close on the physiological as it is on the morphological side, 

 and the fundamental or general physiology of the tissues seems to be every- 

 where the same. Gradually, however, the material for a genuine special 

 human physiology is being acquired. In many directions special investigation 

 upon man is possible; for instance, in the study of the localization of function 

 in the cerebral cortex, or the details of body metabolism as obtained by exam- 

 ination of the excreta, or the peculiarities of vaso-motor regulation as revealed 

 by the use of plethysmography methods, or the physiological optics of the 

 human eye. This special information, as rapidly as it is obtained, is incorpo- 

 rated into the text-books of human physiology, but the fact remains that the 

 greater part of our so-called human physiology is founded upon experiments 

 upon the lower aninals. 



Physiology as a science is confessedly very imperfect; it cannot compare in 

 exactness with the sciences of physics and chemistry. This condition of affairs 

 need excite no surprise when we remember the very wide field that physiology 

 attempts to cover,a held co-ordinate in extent with the physics as well as the 

 chemistry of dead matter, and the enormous complexity and instability of the 

 form of matter that it seeks to investigate. The progress of physiology is 

 therefore comparatively slow. The present era seems to be one mainly of 

 accumulation of reliable data derived from laborious experiments and observa- 

 tions. The synthesis of these facts into great laws or generalizations is a task 

 l.ir i lie future. Corresponding with the diversity of the problems to be 

 solved we find that the methods employed in physiological research are mani- 

 fold in character. Inasmuch as animal organisms are composed either of 

 single cells or aggregates of cells, it follows that every anatomical detail with 

 regard to the organization of the cell itself or the connection between dif- 

 fered cells, and every advance in our knowledge of the arrangement of the 

 tissues and organs that form the re complicated mechanisms, is of imme- 

 diate value to phvsiology. The microscopic anatomy of the cell (a branch of 



