52 THE SCIENCE OF LIFE. 



CHAPTER IV. 

 TISSUE FORMATION. 



In regard to the physical universe, it might be better tc substitute for 

 the phrase " government by laws," " government according to laws," mean- 

 ing thereby the direct exertion of the Divine Will, or operation of the First 

 Cause in the Forces of Nature, according to certain uniformities which 

 are simply unchangeable, because, having been originally the expression of 

 Infinite Wisdom, any change would be for the worse. DR. W. B. CAR- 

 PENTER. 



1. A TISSUE is a structure which presents a special 

 form and serves a special purpose. Thus we find in 

 plants cellular and woody tissues, and in animals muscu- 

 lar, nervous, connective, and epithelial tissues, etc. 

 From tissues are formed organs, as the circulatory, res- 

 piratory, or digestive organs. A collection of organs 

 serving a common purpose is called a system, as the nu- 

 tritive, generative, or nervous systems. The union of 

 systems in a co-ordinate organism, or the equivalent of 

 such a union, forms an individual. An individual among 

 the higher forms of life is a very complex arrangement 

 of systems and organs ; but in the lower forms more 

 simple arrangements prevail, which may be considered 

 equivalent, or representative, of complicated organs, as 

 in the Rhizopods, referred to in Chap. II., Sec. 5. 



2. In the formation of tissues, the peculiar living prop- 

 erties of bioplasm already described ; the physical agen- 

 cies of light, heat, electricity, and moisture ; chemical 

 reactions such as are common to inanimate substances ; 



