WET PREPARATIONS. 397 



juices ; therefore the spirit is almost always dirty, or there is a sedi- 

 ment of coagulated serum at the bottom, so as to require a vast number 

 of shiftings before the whole of the juices are coagulated ; more espe- 

 cially where the parts are not quite fresh. Such spirit as is weak might 

 be improved by dissolving some alum in it. Besides their not coagu- 

 lating the juices quickly enough, they do not coagulate them sufficiently ; 

 most of the preparations that were put up in gin, are in this manner 

 milky, by having the juices partly coagulated and partly suspended. 

 At the second and succeeding times of putting spirits to preparations, 

 it is not necessary that it should be so strong as at the first. Proof 

 spirits lowered one third will be strong enough. 



Of exposing the different parts of a Preparation.- — Besides the exposi- 

 tion of the different parts in the dissection, they should be exposed as 

 much as possible when in the form of a preparation. In the wet 

 preparation, it is often necessaiy to have bristles stretched from one 

 part to another ; bristles put into parts to point them out, as into the 

 ducts of glands, &c. These, if there are many of them in the same 

 preparation, should be of different colours ; black and white we have 

 naturally ; but still it is frequently necessary to have a variety of 

 colours ; bristles take on a bad dye of green, blue, red, &c, but if 

 painted, will do very well. "Where bristles are too small, or too weak, 

 quills may be used, or the hairs of a rhinoceros's tail, &c. 



Such substances, however, are sometimes too short, therefore some- 

 thing else must be substituted, as wire — such as passing it through the 

 body of a snake to give it a particular form, &c, but the wire should 

 not be iron, as it becomes rusty. Brass and copper wire also corrode ; 

 but I suspect something else than spirits, viz. Volat. Alk. or Acid, &c. 

 may do this. 



Of suspending Preparations in Spirits. — The threads by which pre- 

 parations are suspended should be as fine as possible, so as they are 

 sufficient to bear the weight of the preparation, but which need not be 

 so strong as to suspend it in the air, as it is much lighter in spirits. If 

 a preparation is such as to keep its form without threads, and only 

 needs suspension, yet it is best to use two threads; as, in looking 

 at the preparation, it will then turn with the glass. These should 

 be fixed to opposite points of the preparation, or it will not answer 

 so well. 



The threads used for very small light preparations, should be allowed 

 to untwist themselves in water before they are used ; otherwise they 

 will twist themselves in the spirit and become as one thread, which 

 makes all the parts suspended appear indistinct. A single thread of 

 the silk-worm is in general strong enough for most, and does not twist 



