In such instances the tubes hold the same relation to the Haversian canals as do the bone cells where they exist. (Seelig. 456.) The cells when seen by transmitted light,espe cially in a transverse section of bone, appear perfectly opaque ; this has given rise to the opinion that they contain some amorphous salt, and the fact that these same cells become trans parent when the bone has been subjected to the action of acid, confirmed observers in this opinion, and that this salt was a salt of lime. When first these observations were commenced? I was disposed to ho1d a like opinion, but fur ther investigation has convinced me that as a rul the cells are empty. I have seen, and that t very frequently, cells which were o . .
viously without contents, and thi observation may be repeated in any' bone where the cells are tolerably. large by making a section in the length of bone, and so parallel with the direction of most of the I Iave canals. By making such a se you expose the cells in their larg diameter, when they maybe seen into; whereas if cut through in their narrow diatneter they are so deep that they0 produce complete interference of light, and so seem black, as though filled with some opaque substance.
Again, if turpentine or thin Canada balsam be added to a section quite dry beforehand, the dark cells will become filled with turpentine or bal sarn, and so become transparent.
The function performed by the bone cells is no doubt that of circulation.' Atmospheric pressure would prevent them from remaining empty, and as tbeir openings are always upon a surface where there are bloodvessels, _ _ _ _ .
the fluid portion of the blood IS prO bably carried into them. Supposn5 _ _ them oncefilled with liquor sanguinis, the varying density of the blood itself v,-ould produce a slow kind of circu lation, even though the contents of the cells remain unaltered, which is not probable.
Cells of smaller form and having branching tubes are to be found in the vegetable world. The shells of' various fruits, as the cocoa-nut, peach, common nut, &c. present cells so like those of bone that a section of shell has often been mistaken for one of bone. In this instance they also answer the purposes of circulation. .
The growth of bones.—Many experiments have been made to ascertain the mode of growth in bones, but they have given as their results the direction of increase rather than the process of interstitial grovvth. The experiments alluded to are commonly spoken of as the madder experiments, and were instituted by Du Hamel, Detlif, Hunter, Stanley, Paget, and others.
It was discovered that phosphate of lime acts upon the colouring matter of madder as a mordant. Thus, if phosphate of lime be pre cipitated from a state of chetnical combination in a solution of madder, the colouring matter of the madder is carried down with the phos phate in a state of chemical combination, itn parting to the phosphate a red colour, which is not diminished by repeated washing, but gra dually fades by exposure to light. But, before this discovery was made, it was found that the bones of some pigs that had been accidentally fed upon madder were rendered red. Atten tion having been drawn to this curious fact that madder given in the food reddens the bones of the animal, the madder experiments were undertaken, and led to the following results.
If madder be given to a growing animal, and the bones be examined by making a sec tion of a cyllndrical bone, a ring of reddened bone will be seen to form the circumference of the bone, and a similar reddened ring to form the parietes of the medullary cavity. If in this experiment the animal had been old, these rings of red would not have been seen, or, if seen, only very faintly. From these two ex periments it has been deduced that the bone, or rather the phosphate of lime, which has , been deposited during the exhibition of the madder, has alone been reddened.
if, however, after giving madder to a grow ing animal for a time, its use be discontinued for a while and then be again given, several rings of reddened hone vvill be observed on making a section of a cylindrical bone, that is, reddened bone will be deposited during the use of the madder, and white bone at the interval of its discontinuance. So that, by the alter !nate use and disuse of madder, rings of red slid of white bone will be formed to a consi derable number. From these experiments it has been deduced that bones increase in their Ammeter by the development of the bone on the surface somewhat in the same manner that ?. crystal increases in size by additions to its surface.
! Air. Gibson, however, for a while threw some I joubts On the value of the madder experiments ! Ind the deductions from them, by stating that serum of the blood had an affinity for the colouring matter of inadder superior to that of the phospbate of lime, aiid that the bone became stained only after the serum had been tho roughly saturated with madder, and more, that the serum, from the discontinuance of madder in the food, or losing the colouring matter, absorbed that existing in the bones.