Mr. Paget has, however, proved that the affinity is far stronger between phosphate of lime and the colouring matter of madder than between serum and the latter. These experi ments seem at first sight far more valuable than a closer investigation will prove them to be, as will be seen on considerina the following fact, namely, that not only is the surface of the bone with the walls of the medullary cavity tinged red by the exhibition of madder, but also the cir cumference of every Haversian canal through out the bone, in fact every surface that lies in contact with a vessel or vessels. The fact that every Haversian canal has its coloured ring had escaped observation, as these experimenters had been limited to the use of the naked eye, whereas the Haversian canals, with their co loured rings, are only seen by the use of the microscope.
It therefore remains for observation to be made upon the effects of chnsecutive feeding with and without madder, upon the Haversian canals, before any very accurate deductions can be made.
Other experiments have been tried in inves tigating the growth of bones.
Rings of metal have been lightly fixed round a long bone, which after a while has been found to contain the rings in its medullary cavity, from which it has been inferred that the bone has grown by additions to its circumference, while the medullary cavity has been enlarged by the absorption of the bone forming its parietes. These experitnents, which were made by Du Hamel, have been confirmed by Hunter and Stanley.
Experiments of a similar nature have been made to determine the manner of growth in the length of bones. Thus holes have been bored in the tibia of a dog at definite intervals, which intervals after the lapse of some days, have been found altered in the relative leng,ths. The intervals near the ends of the bone have in creased considerably, while those situated near the centre of the bone have scarcely changed. Mr. Stanley has shown that in some animals the growth is greatest at the distal end, while in other animals it is greater toward the proximal end of a long bone.
In the two experiments which I have related in a previous part of this article the walls of the medullary cavity were as distinctly reddened as the circumference of the bone, and the cir cumference of each Haversian canal as either. These would therefore prove too much for the theory which supposes that a long bone in creases its diameter by the depositions upon its surface and under its medullary cavity by the absorption of the walls. Supposing the idea that phosphate of lime, which is deposited during the exhibition of madder, is alone red dened to be correct, the parietes of medullary cavity should not show colour, as here absorp tion is supposed to be going on.
From what is already known, I think that the bones are coloured by the madder just in proportion to their powers of imbibition, Nvhich Nvill be in inverse proportion to the. amount of phosphate of lime which they contain.
As regards the growth of bone, the laws common to the growth of every other tissue and to the whole body will, I think, be found to hold good. And the growth of these organs will be found to be interstitial, pervading the whole substance, though the action will be more energetic at some points than at others, as the neighbouring org,ans may require greater length or breadth in one direction than in an other.
The younger the bone the more rapid will be its growth, but this law is common to all the tissues. The increase of length of a long bone
at the epiphysis must not be confounded with growth of the bone, for here, so long as car tilage connects the shaft with the epiphysis, osseous tissue is being developed; whereas, in speaking of the growth of bones, the increase of the tissue alreacly developed is alone meant.
Of the developement of osseous tissue.—As the developement takes place in cartilage, and as the cartilage undergoes some change pre vious to its giving place to bone, it vvill be well to give a slight sketch of the structure of temporary cartilage before going into the for mation of the more permanent tissue. The rudimentary condition of cartilage rnay be best examined in the fcetal chicken, a few days after the commencement of incubation. The exact time for making the observation will be found by taking an egg for examination every six hours, commencing after the eggs have been exposed to the due temperature for thirty-six hours. On the first appeamnce of the verte bral column, which will present a semitrans parent line in the length of the developing fcetus, the whole must be removed with great care to the field of the microscope. This part of the operation requires some care, but with a little management may be successfully performed. I found but little difficulty in removing the delicate object after adopting the following plan. Having, in the first place, placed the egg in a dish of water of sufficient depth to cover it, let the shell be carefully removed ; then, by moving the water with the assistance of a camel's-hair brush, take away the albumen so as to leave the yelk free. The point where deve lopement is going on will then be sufficiently conspicuous. At a considemble distance around this the membrane of the yelk should, with a pair of sharp scissors, be cut through, and carefully separated with the aid of a camel's hair brush and a pair of forceps. This having been effected, the subject for examination will be left on the surface of the yelk, and may, with delicate manipulation with the pencil, be removed to a slip of glass held near it under the surface of the water. Ilaving completed your purpose so far, the glass must be raised very slowly from the water, so that the spe cimen may not float off, and this being covered with a little thin talc or glass supported at the sides, so that it shall not press upon the em bryo to be removed to the field of the micro scope. If the specimen be favourable, the semitmnsparent line of the vertebral column will under a low power appear made up of a vast number of clear colourless oval cells, so closely connected as to leave no appreciable space between the individuals composing the mass. Under a higher power, however, each cell will present a definite outline with a central nucleus or nuclei, and even in some nucleoli. The cells give the appearance of density and clearness of substance, and Nvith their definite and smooth outline present a great contrast to the highly granular cells of developement that surround them. In each vertebra there is some show of a radiate arrangement, for many cells are egg-shaped, and have their small ends placed towards the centre of the growing mass. At this period of the formative process the cells are so close to each other that there is no space for intercellular tissue.