16 GENERAL PHYSIOLOGY. 



rived from cells, have preserved these properties. The irrita- 

 bility of Glisson and Haller, the incitability of Brown, the 

 excitability of Tiedemann, are precisely the characteristic 

 property of the cell, and in this point of view the exact 

 expression that the essence of vital phenomena represents 

 to us. 



It is due then to the powerful means of study furnished by 

 the microscope that we owe the idea that we are formed 

 from vital phenomena ; but it would be unjust not to men- 

 tion in this connection the name of Bichat, who, by his en- 

 dear ors in the study of general anatomy, pointed out the 

 fact that the foundation of the science of histology should 

 be established by means of micro-graphy. The introduction 

 of the microscope in the seventeenth century in the hands 

 of Malpighi and Leeuwenhoek resulted more in observa- 

 tions of simple curiosity than in scientific researches, at least 

 for the study of animal tissues. At the commencement of 

 this century, Bichat founded general anatomy, and aimed at 

 the study and classification of the human tissues ; but making 

 use only of dissections by the unaided eye, of chemical re- 

 actions, and of physiological and pathological investigations, 

 he could grasp but a few of the gross characteristics that 

 distinguish the tissues. But as soon as the path had been 

 pointed out, and the microscope was established for the re- 

 search of organic elements, Schwann was enabled in 1839 to 

 attempt the study of the tissues, by starting with the cell 

 and founding histology, or what might be called general 

 anatomy studied by means of the microscope. Physiology 

 and Pathology were the necessary consequence. 



HI. DIFFERENT KINDS OF CELLS. THEIR PARTICULAR FUNC- 

 TIONS. DIAGRAM OF THE ORGANISM. PLAN OF STUDY OP 

 PHYSIOLOGY IN THIS TREATISE. 



AT its origin an organism is formed of a single cell, the 

 ovum, which has already been mentioned, and whose segmen- 

 tation has also rapidly been described, as a type of gener- 

 ation or of proliferation of the class of globules in general. 

 From the segmentation of the viteUus, or contents (proto- 

 plasm) of the ovum, the envelopirg membrane, or zona pel- 

 lucida, is formed, enclosing a large number of globules 

 resembling each other ; but after a while these globules begin 

 to vary in their form and position. 



