2 VETERINARY PHYSIOLOGY 



definite organs which they described in detail, and thus 

 prepared the way for the work of Harvey, which led to such 

 important discoveries, and which established the relationship 

 of function to organ. 



The connection between organ and function having been 

 demonstrated, the question of why these various functions are 

 connected with the respective organs — why the liver should 

 secrete bile and the biceps muscle contract, next forced itself 

 upon the attention. 



Tissues and Function. — Again anatomy paved the way 

 to the explanation. The dissecting knife and the early and 

 defective microscope showed that the organs are composed 

 of certain definite structures or tissues, differing widely from 

 one another in their physical characters and appearance, and, 

 as physiologists soon showed, in their functions. By the 

 end of the seventeenth century Leuwenhoek and Malpighi 

 had so advanced the knowledge of the tissues that Haller, in 

 the middle of the eighteenth century, was able to indicate 

 that the function of an organ is really the function of the 

 tissue of which it is composed. 



Early in the nineteenth century Johannes Miiller, taking 

 a comprehensive survey of a great mass of observations which 

 had accumulated, and adding to them the results of his own 

 investigations, created the modern science of physiology. 



Cells and Function. — Physiologists and anatomists alike 

 devoted their energies to the study of these various tissues, 

 and, as the structure of the microscope improved, greater and 

 greater advances were made in their analysis, till at length 

 Schwann was enabled to make his world-famous generalisa- 

 tion, that all the tissues are composed of certain similar 

 elements more or less modified, which he termed cells, and 

 it became manifest that the functions of the different tissues 

 are dependent on the activities of their cells. 



The original conception of the cell was very different 

 from that which we at present hold. By early observers it 

 was described as composed of a central body or nucleus, 

 surrounded by a granular cell substance with, outside all, a 

 cell membrane. As observations in the structure of the cell 

 were extended, it soon became obvious that the cell membrane 



