TISSUES OF THE BODY. 399 



produce the several organs and apparatuses of the body. These organs, 

 whose performances are dependent on the individual qualities of the 

 various tissues of which they are composed, present far greater difficulties, 

 as regards their classification, than the tissues themselves ( 64), the 

 more so, as we are unable accurately to define what is precisely meant 

 by an organ. If we compare the many apparatuses of the body, we find 

 the greatest differences existing as regards their construction. Some of 

 them are formed in the simplest manner of one single tissue, as, for 

 instance, the nails, the lens, the vitreous humour. Their performances, 

 in such cases, may also agree with the physiological energy of the tissue. 

 Other organs, however, are combinations of several, of many, nay, even of 

 most, of the tissues of the body. It will suffice to point, by way of 

 example, to the organs of vision. Thus, here, as in the classification of 

 tissues, the systematic worth of the terms simple and compound seem to 

 recommend them for use. This principle of division, however, can be by 

 no means so strictly adhered to here, owing to the multitude of organs, as 

 was the case in dealing with the tissues. 



It is a common mode of classification among anatomists to group 

 the organs of the body in particular systems. By this we understand 

 the arrangements of parts together, which are found to be identical or 

 similar as regards the finer composition of their tissues. Thus the 

 present divisions into nerves, muscles, osseous, and vascular systems have 

 been arrived at. We also speak, however, of a digestive and generative 

 system, where this similarity of texture in the various parts making up 

 the whole by no means exists. Thus in the many manuals which treat 

 of these subjects the greatest differences as regards classification may be 

 observed. 



It may be found most expedient, then, if we base the third section 

 of this work upon the principle of physiological classification, and make 

 use of the old division of organs, into those which take part in the 

 vegetative occurrences of the body, and those belonging to the animal 

 side of life. It cannot be denied, however, that this classification will 

 not everywhere hold good; for in the wonderful linking of parts one 

 with another there occur many intermediate forms. Thus nerves and 

 muscles make their appearance in apparatuses belonging to the vege- 

 tative sphere, blood and lymphatic vessels, and glands in animal organs, 

 and so on. 



Starting from this point, then, we come to another mode of grouping parts, 

 namely into apparatuses, that is, a combination of a number of organs for 

 the carrying out of some one physiological purpose. A system and 

 apparatus may correspond, as in bony, muscular, and nervous portions of 

 the body, but do not necessarily. Thus from one point of view there is 

 such a thing as a digestive and respiratory apparatus, but not a diges- 

 tive and respiratory system. 'The following is our classification of 

 organs : 



A. Belonging to the Vegetative Group. 



1. Circulatory apparatus. 



2. Respiratory apparatus. 



3. Digestive apparatus. 



4. Urinary apparatus. 



5. Generative apparatus. 



