SCOPE AND AIMS 15 



matters are now highly skilful and accurate. 

 Histology has both a morphological side, in 

 as far as it deals with form, and a physiological 

 when it treats of the functions performed by 

 these tissues. Further, much information is 

 furnished to the physiologist by the examina- 

 tion of the body at various stages of growth, 

 and more especially in the earlier stages. 

 Thus the study of the formation and early 

 development of the embryo, and tracing the 

 origin of the tissues, and the gradual building 

 up of the more complicated organs, have > 

 thrown light on vital phenomena. This line ' 

 of research is known as Embryology. 



The body is also the theatre of many 

 phenomena of a chemical character ; indeed 

 it may be said that the phenomena of life 

 depend essentially on chemical changes. As 

 we shall see, food and oxygen are introduced 

 into the body, and, by chemical changes, 

 often of a complicated kind, many chemical 

 substances are formed, some of which are built 

 into the tissues, while others are thrown out 

 as effete. Many of the operations in the 

 digestion of food and in the formation of 



