Ryder.] Ob'2 [Nov. 1, 



bony tissues proper. The matrix being firm and stable there is no close 

 and continuous union with the vascular system except by way of the net- 

 work of processes of the so-called osteoblasts or "bone-forming cells," 

 which indirectly form one system with the Haversian systems of blood 

 and lymph vessels in the higher types. In the lower types and in em- 

 bryos this is not the case ; the bone matrix as a plate or delicate reticvilum 

 (vertebrae of sharks) calcifies without even the presence of so-called osteo- 

 blasts embedded in its substance. The calcification of the homogene- 

 ous concentrically laminated cj^sts, containing parasitic Trichinte in 

 infested muscle, the cysts being the result of the defensive action of the 

 connective tissues and vessels against the parasites, is surely proof that 

 calcification is a physical process determined merely by the presence of an 

 ametabolic or stable colloidal matrix, which is capable of taking up cal- 

 careous or other earthy salts, the latter losing their crystalline characteris- 

 tics more or less completely, owing to the physical interference of the 

 colloid in the pi'ocesses of crystallization. 



In young sharks, eight inches long, the lower jaw is instructive in this 

 connection. Cross sections of it show that the calcareous salts have been 

 deposited on the superficial layers of the matrix of Meckel's cartilage as 

 irregular nodules, many of which recall some of Rainey's figures of crys 

 talloids formed in artificially prepared and calcareously saturated colloids. 

 These nodules in the young shark's jaw are, moreover, nearest the surface 

 of the cartilage or nearest the vascular source of calcareous deposit. In 

 developing bone the same holds true. It is in the middle or diaphi'sial 

 part of the cartilage of a foetal long bone in which endocartilaglnous cal- 

 careous deposits are first to be observed, or in the oldest part of the car- 

 tilage or that in which the colloidal matrix has had the most time in which 

 to passively take up such materials. Later this calcareous material is 

 again absorbed when the cartilage of the shaft is eroded and destroyed by 

 the ingrowth of the blood-vessels, at the time the formation of the matrix 

 of tbe true bone is to begin. 



Summing up the whole of this evidence, we are fully warranted in 

 drawing the following inferences : 



1. That a dense homogeneous, ametabolic or passive colloidal matrix, 

 whetlier found within or without a living body, will tend to abstract anil 

 precipitate within itself, in the form of nodules or granules, any calcare- 

 ous salts with which it may be mixed or by which it is bathed. 



2. That the density of these colloidal matrices greatly increases their 

 avidity for calcareous matters, so as to cause them to very soon become 

 completely saturated with the calcareous salts so as to appear homogene- 

 ous, and characterized by a mineral-like brittleness, as in the laminar 

 bones of fishes, without included osteoblasts, or as liappens in the case of 

 the dense matrix of the true bone tissues of liighcr animals. 



3. That the firmness and persistency of the bones of higher forms are due 

 to the presence of their matrix of collagen-like material to and through 

 which the calcareous materials are being continually brought by the 



