H. The nerve-corpuscle, the centre of nervous power.

I. The mucous tissue, as Virchow calls it, common in embryonic structures, seen in the vitreous humor of the adult.

To these add X, granules, of indeterminate shape and size, Y, for inorganic matters, such as the salts of bone and teeth, and Z, to stand as a symbol of the fluids, and you have the letters of what I have ventured to call the alphabet of the body.

But just as in language certain diphthongs and syllables are frequently recurring, so we have in the body certain secondary and tertiary combinations, which we meet more frequently than the solitary elements of which they are composed.

Thus A B, or a collection of cells united by simple structureless solid, is seen to be extensively employed in the body under the name of cartilage.  Out of this the surfaces of the articulations and the springs of the breathing apparatus are formed.  But when Nature came to the buffers of the spinal column (intervertebral disks) and the washers of the joints (semilunar fibrocartilages of the knee, etc.), she required more tenacity than common cartilage possessed.  What did she do?  What does man do in a similar case of need?  I need hardly tell you.  The mason lays his bricks in simple mortar.  But the plasterer works some hair into the mortar which he is going to lay in large sheets on the walls.  The children of Israel complained that they had no straw to make their bricks with, though portions of it may still be seen in the crumbling pyramid of Darshour, which they are said to have built.  I visited the old house on Witch Hill in Salem a year or two ago, and there I found the walls coated with clay in which straw was abundantly mingled;—­the old Judaizing witch-hangers copied the Israelites in a good many things.  The Chinese and the Corsicans blend the fibres of amianthus in their pottery to give it tenacity.  Now to return to Nature.  To make her buffers and washers hold together in the shocks to which they would be subjected, she took common cartilage and mingled the white fibrous tissue with it, to serve the same purpose as the hair in the mortar, the straw in the bricks and in the plaster of the old wall, and the amianthus in the earthen vessels.  Thus we have the combination A B C, or fibro-cartilage.  Again, the bones were once only gristle or cartilage, A B. To give them solidity they were infiltrated with stone, in the form of salts of lime, an inorganic element, so that bone would be spelt out by the letters A, B, and Y.

If from these organic syllables we proceed to form organic words, we shall find that Nature employs three principal forms; namely, Vessels, Membranes, and Parenchyma, or visceral tissue.  The most complex of them can be resolved into a combination of these few simple anatomical constituents.