PART II. 



HISTOLOGY. 



DEFINITIONS, SUBDIVISIONS, ETC. 



HISTOLOGY 1 is the scientific classification and description of the 

 structural 2 or organized elements of the solids and fluids of living 

 organisms. Since these elements can be demonstrated only by 

 the aid of the microscope, Histology is one of the subdivisions of 

 minute or microscopic anatomy. 3 It also includes Histogeny, or the 

 development of the elements just mentioned. 



Animal Histology, Yegetable Histology, and Human Histology, 

 are terms requiring no special explanation. Comparative Histology 

 is the study of the structural elements of the lower animals. Pa- 

 thological Histology is the study of the minute structure of the 

 organism as modified by disease. 



If we investigate the structural elements in their general rela- 

 tions only, and without regard to their distribution in particular 

 parts or organs, this is General Histology ; if in regard to the latter 

 particulars, it is Special Histology. 



Thus explained, the present is a treatise on Human Histology, 

 both general and special, and, at the same time, both physiological 

 and pathological. Thus the subjects it includes will be found to 



1 From 'ta-To?, a web or network, and \oyof, description. 



2 "Morphological elements" is a phrase sometimes employed in the same sense. 



3 Histology may, indeed, be regarded as general microscopic anatomy. If we 

 investigate microscopically merely the structure of a part or organ, without any 

 ulterior object, this is special microscopic anatomy. And if we thus investigate 

 the structure of the various organs with the view to establish their functions, or 

 scientifically to associate the latter with the structure, we are contributing to the 

 department now known as physiological anatomy. 



