GENERAL CONSIDERATIONS. 3 



GENERAL IDEA OF THE ORGANISATION OF ANIMALS. 



Order followed in studying the Various Apparatus. 



The bodies of animals, formed of organised matter, contain fluids and 

 solids. 



The fluids are very abundant in the animal economy ; not only do they 

 fill certain vessels constructed for them, but they also impregnate all the 

 solid parts of the body. Their importance is very great, for without them 

 the organic solids would perish ; an element deprived of humidity is an 

 element deprived of life. 



Fluids vary in their nature and composition. Apart from those that 

 the solids imbibe, there is not one which is completely amorphous. In the 

 midst of a liquid holding organised matter in solution there are always 

 elements which will be referred to hereafter. Examples : the blood and lymph. 



In studying the organic solids, we will proceed from the simple to the 

 complicated. 



ELEMENTS. Solid organised matter presents itself in the form of more or 

 less voluminous particles, in every instance invisible to the naked eye, and 

 named the anatomical elements. They may be reduced to three principal : 

 the granule, cell, and fibre. 



Granules. These are the smallest known elements. They may' be held 

 in suspension in animal fluids, remain free among the other elements, or be 

 enclosed in the interior of cells. Their nature is not always the same : 

 they are proteic or fatty. They are called pigmentary when they exhibit 

 a brown colour. 



Cells. The cell is pre-eminently the anatomical element. 



It may be represented to the mind as a microscopic collection of a 

 nitrogenous substance, viscid or slightly granular, and endowed with extreme 

 vitality. Frequently in the midst of this protoplasm (for so it has been 

 called), there is perceived a nucleus provided with a nucleolus, and at its 

 periphery an enveloping membrane is discovered. It must not be forgotten 

 that this membrane, and even the nucleus, is necessarily a constituent portion 

 of the cell. 



The cell lives like an entire organism : it feeds, grows, multiplies, 

 absorbs, secretes, moves, etc. It behaves like a complete animal, though it 

 be a microscopic one. 



The form of the cell varies greatly, as does its volume and its nature. 

 It has therefore received various names. 



There are round, polyhedral, fusiform, stellate, and other shaped cells. 

 Some have a diameter of l-12000th part of an inch, while others are l-2000th 

 part. Cells multiply in various ways : 1st, by the division of the nucleus 

 and segmentation of the protoplasm in the interior of the enveloping 

 membrane (endogenous multiplication) ; 2nd, by constriction, the division 

 of the nucleus, protoplasm, and enveloping membrane (fissiparous multipli- 

 cation) ; 3rd, by a kind of bulging or swelling of the enveloping membrane, 

 and strangulation and separation of the enlargement thus formed 

 (gemmation). 



A large number of cells only temporarily remain in this condition. In 

 consequence of modifications that cannot be referred to here, they are con- 

 verted into fibrillee or other elements, in which it is difficult to recognise 

 them. 



Others maintain the cellular form : then they are developed, live, and 

 die in several ways. Sometimes they are worn by the contact of foreign- 



