CHARACTERS OF ANIMALS. 123 



remained for some time, and substitute a fresh portion in 

 its stead. If the object has remained a sufficient length of 

 time, the different layers of which it consists will separate 

 easily, and a structure will be developed, which its original 

 appearance would not have led one to expect. 



The principal use of maceration in water is to separate 

 the softer parts, and to expose the denser framework of the 

 organs. It is, however, in many cases expedient to reverse 

 this process, to abstract the hard parts, with the view of ob- 

 serving the distribution of the softer parts. The macerat- 

 ing fluid employed in this case is an acid, usually the mu- 

 riatic, diluted with water, as this menstruum exercises but 

 a feeble action on the soft parts. When bones, shells, or 

 corals, are steeped in a fluid of this kind, the earthy matter 

 is abstracted, and the cartilaginous basis is ^^left behind, 

 exhibiting in its arrangement its mode of growth and inti- 

 mate structure. 



Frequently, the organs are so much covered with fat, 

 as to be concealed from the view of the observer, and to be 

 in a great measure protected from the action both of wa- 

 ter and acids. In such cases, oil of turpentine is usually 

 employed, in which the fat readily dissolves. This method 

 was successfully employed by Swammekdam, in his exami- 

 nation of the viscera of insects. 



2. Coagulailon. — Many small animals, and some of the 

 parts of larger animals, are so soft and tender, as scarcely 

 to admit of examination in their natural state. In some 

 cases they are exposed to cold and suffered to freeze. In 

 general, however, the requisite degree of firmness is com- 

 municated to them, by immersing them in alcohol or vi- 

 negar. In many cases, in attempting to trace the course 

 of vessels, their walls are found so thin, and their contents 



