PROCESS OF BLOOD-FORMATION. 91 



On the Blood Formation. Besides growth and 

 absorption, the third general element of vital action in 

 individuals of the higher orders is the preparation of 

 the special pabulum, on the immediate conversion of 

 which into living matter all continuance of life de- 

 pends. On this subject I will only touch upon the 

 points in which Beale's protoplasmic theory differs 

 from the views previously held by physiologists. The 

 elaboration of the blood to a state fit for pabulum to 

 the higher tissues is performed by a series of proto- 

 plasmic masses of special, but lower, endowments than 

 those of the higher tissues. While passing through 

 these the crude nutriment is entirely decomposed, and 



bone is exposed to irritation or pressure, as in the case of aneurism, or 

 physiologically in the jaw during the formation of the tooth-sac, large, 

 many-nucleated cells make their appearance. Wherever these are in 

 contact with the bone a portion is eaten away, and what were before 

 known as the lacunae of Howship are formed. By this process of 

 lacuna-formation the bone is gradually cleared away before the ad- 

 vancing tooth-sac, or other irritating cause which is producing its- 

 absorption. What is specially of interest to us in showing that, even 

 in the living body, the true bone substance is actually dead, is the fact 

 noted by Kolliker that the ivory pegs driven into the bones in the living 

 subject in Dieffenbach's operation for pseudo-arthrosis were found to be 

 covered with the typical lacunse of Howship filled with the many- 

 nucleated giant cells. And, besides, in many places human bone- 

 substance was deposited on the eroded surface of the animal ivory. 

 This corresponds to what is observed in the growth of the tooth-sac ; 

 for after the irruption of the tooth, the giant cells disappear, and the 

 osteoplasts, or formative bone protoplasm masses, again clothe the 

 surface of bone, whose formation, instead of absorption, again proceeds. 

 This leads us to the origin of these cells, and we find that Kolliker con- 

 siders they belong to the same category as the osteoplasts or formative 

 cells of bone, and proceed directly from them ; that there is a trans- 

 formation of the one into the other by division ; and that they may be 

 seen in transition stages. Dr. Morison has also seen intermediate 

 forms : " and also osteoclasts (giant cells) lying in close apposition on 

 the one hand to the border of absorbing bone, and on the other to a 

 twig of capillary vessel." See " Bone Absorption by means of Giant 

 Cells," by Dr. A. Morison, "Edinburgh Med. Journal," Sept. 1873. 



