20 DR. G. THIN. 



physiological connection of the structure with the living 

 organism has ceased to exist. The strongest objection that 

 could be raised against this interpretation of " giant cells " 

 — namely, want of proof that layers of flat cells exist — is 

 answered completely as far as cartilage is concerned by the 

 observations recorded in this paper. KoUiker does not 

 bring forward a single argument in support of his hypothesis 

 that giant cells or osteoclasts are actively concerned in the 

 absorption that takes place in growing bone, except that they 

 are found on surfaces in which absorption is taking place, a 

 fact which finds a much simpler interpretation on the 

 hypothesis that they are a product of the absorption. That 

 they are found in ossification that is taking place where there 

 is no cartilage to absorb does not materially aff'ect the argu- 

 ment when it is admitted that they exist in cartilage. 

 Hitherto layers of flat cells have been as little suspected to 

 exist in cartilage as in bone. But even in bone the author 

 relies on more than mere analogy in believing them to exist. 

 He succeeded on one occasion in isolating by potash from the 

 shaft of a frog's femur great numbers of oval cells, and on 

 several occasions he has seen on fragments of bone treated by 

 the solution numbers of round nuclei, the distribution of 

 which corresponded with the supposition that they belonged 

 to cells w^hose outlines were imperfectly visible, but w^hich 

 in so far as they could be seen suggested an epithelial 

 arrangement. 



In regard to the " giant cells " found in pathological pro- 

 cesses it is highly probable, in the light of the above observa- 

 tions, that they are simply fragments of altered and 

 disintegrated membranes, covered with flat cells such as are 

 present in all connective tissues. 



If the author maybe allowed with difiidence to express an 

 opinion in regard to an appearance that has been studied 

 by so many eminent observers, he would suggest that many 

 of the giant cells (osteoclasts) found in the marrow of young 

 bones present when examined under the microscope (no 

 regard being had to any theory) the characters of eff'ete and 

 disintegrating tissue. 



It remains to consider what relation the structures above 

 described have to the spaces knoAvn as cartilage " capsules " 

 and their contained cells. As has been already stated, 

 fragments of cartilage can be isolated from a mass treated 

 by the potash solution in which a series of concave depres- 

 sions are distributed in perfect analogy with the distribution 

 of the " capsules." A so-called capsule consists of two such 

 concavities being applied to each other in such a way that 



