ORGANIC MATTEH. 11 



structures principally implicated in the physiological pro- 

 cesses to be explained; and, in particular, it will be necessary 

 to describe the textures or tissues of the different parts, which 

 in great measure require the aid of the microscope for their 

 examination. This is the department of anatomy termed 

 Histology. 



2. Living bodies are termed Organisms, because they are 

 composed of organs, or parts devoted to different purposes ; 

 and the purpose to which any organ is devoted is called its 

 function. 



Organs are of various degrees of complexity. In organisms 

 of the higher or more complicated description, bodies com- 

 parable with organisms of a very simple or rudimentary kind 

 exist as textural elements. Such textural elements enter into 

 the formation of more complex textural organs (e.g., arteries 

 in animals, and vascular bundles in plants), which are dis- 

 tributed as component parts of a variety of special organs, 

 such as eye, ear, liver, brain, etc., often the only parts alluded 

 to when the term special organ is used. 



3. All organisms are in great part composed, particularly 

 their more active portions, of chemical combinations of a 

 complex kind, called organic matter, together with which 

 there are always, in addition, various mineral constituents 

 and water entering into their composition. The most dis- 

 tinctive character of organic matter is that it is combustible, 

 becoming black when heated over a flame ; and, as this 

 blackness is due to carbon, it disappears on further exposure 

 to heat and air, leaving the ash or non-volatile mineral 

 constituents which are always associated with organic matter. 



Organic matter is divisible into two groups of substances, 

 which are distinguished as nitrogenous, and non-nitrogenous 

 or carbonaceous; the first containing carbon, hydrogen, 

 oxygen, and nitrogen, and the second having no nitrogen in 

 their constitution. The products of the complete combustion 

 of carbonaceous matters are carbonic acid and water, while 

 nitrogenous substances yield ammonia in addition. 



The attraction of both carbon and hydrogen for oxygen is 

 very great. Carbonic acid, consisting of one equivalent or 

 combining proportion of carbon and two of oxygen, is the 

 compound which is formed when carbon is freely exposed to 



