THE LARGER BLOODVESSELS. 141 



coat, shreds of the middle coat nearly always adhere 

 to it, and the muscular cells of this readily separate 

 after the maceration in bichromate. But the isolated 

 cells present in most instances such a ragged shape- 

 less aspect that they would hardly be known for 

 muscular tissue. A convincing proof, however, is 

 the addition of a little weak logwood solution at 

 the edge of the cover-glass. This, as it comes to 

 each of the cells in question, almost instantaneously 

 stains their long rod-shaped nuclei of an intense 

 violet, whilst the body of the cell, if the logwood 

 solution be sufficiently weak, remains uncolored. 

 The addition of a little glycerine at the edge of the 

 cover-glass, and the subsequent cementing, are suffi- 

 cient to preserve the preparation. 



The connective tissue and elastic fibres of the outer 

 coat (as well as the muscular tissue of the same coat 

 in certain veins) can be equally well seen in a teased- 

 out preparation. 



Preparation 3. Study of the structure of the 

 bloodvessels by means of sections. To form a 

 correct idea of the relative thickness of the several 

 coats, as well as to observe the differences in arrange- 

 ment in different arteries and veins, it is necessary 

 to study them in vertical sections, f.^., sections made 

 in a direction at right angles to their surface. Such 

 sections may be either transverse or longitudinal ; it 

 will be better perhaps to choose the former direction, 

 for the middle coat is thereby better displayed. But 

 the vessel to be cut must tirst be hardened. This 

 may be effected speedily by immersing it in very 

 strong spirit for a day or two, and indeed this method 

 can be employed tor nearly all the tissues and organs. 

 It is preferable, however, in many instances to effect 

 the process more slowly, by means of some watery 

 fluid, such as a strong solution of bichromate of 

 potash or a weak solution of chromic acid, since in 

 this way the parts shrink less and consequently 

 retain their form better; the process should, never- 

 theless, always be completed by means of spirit. In 



