ANATOMICAL SYSTEMS. 37 



the air in the 1-ungs from time to time; and the act of 

 breathing is \ the final result of the activity of the whole 

 apparatus. 



Many similar instances, as the alimentary apparatus, the 

 auditory apparatus, and so on, will readily be thought of. 

 The study of the working of such complicated mechanisms 

 forms a very important part of physiology. 



Anatomical Systems. From the anatomical side a 

 whole collection of bodily organs agreeing in structure 

 with one another is often spoken of as a system; all the 

 muscles, for example, are grouped together as the muscular 

 system, and all the bones as the osseous system, and so on, 

 without any reference to the different uses of different 

 muscles or bones. The term system is, however, often used 

 as equivalent to " apparatus:" one reads indifferently of the 

 " circulatory system" or the "circulatory apparatus." It 

 is better, however, to reserve the term system for a collec- 

 tion of organs classed together on account of similarity of 

 structure; and "apparatus" for a collection of organs con- 

 sidered together on account of their co-operation to execute 

 one function. The former term will then have an anatomi- 

 cal, the latter a physiological, significance. 



The Body as a Working Whole. Finally it must all 

 through be borne in mind that not even the most complex 

 system or apparatus can be considered altogether alone as 

 -an independently living part. All are united to make one 

 living Body, in which there is throughout a mutual inter- 

 dependence, so that the whole forms one human being, in 

 whom the circulatory, respiratory, digestive, sensory, and 

 other apparatuses are constantly influencing one another, 

 each modifying the activities of the rest. This interaction 

 is mainly brought about through the conductive and co- 

 ordinating tissues of the nervous system, which place all 

 parts of the Body in communication. But in addition to 

 this another bond of union is formed by the blood, which 

 by the circulatory apparatus is carried from tissue to tissue 

 and organ to organ, and so, bringing materials derived in 

 one region to distant parts, enables each organ to -influence 

 all the rest for good or ill 



