On Erosion of the Surface of Glass, &c. By Dr. W. M. Ord. 765 



tion " has always seemed to me to have an importance as great as 

 that of his chapters on " Molecular Coalescence." The two together 

 presented a beautiful correlation, enabling one to follow the build- 

 ing up of skeletal formations in the first place, and their adapta- 

 tion to altered conditions of growth and repair in the second. 



In bone, for example, we could see, in principle, how the struc- 

 ture of the first Haversian systems was determined by the law of 

 molecular coalescence ; how the earthy matters deposited in colloid 

 ground-substance ceased to show crystalline form and were moulded 

 into laminae wherein the organic and inorganic matters were 

 intimately mingled and distributed. We could see in it by the 

 Hght of the principle of molecular disintegration the formation of 

 Haversian spaces, as a part of remoulding and repair. May I for 

 a moment step aside to remind you of what Mr. Eainey meant by 

 this expression, " molecular disintegration " ? He meant this — 

 that when spheres of carbonate of lime, or spheres of mixed 

 carbonate and phosphate, had been formed in a matrix of gum, and 

 were afterwards transferred to a fresh solution of gum of the same 

 kind as that first used, they lost their sharp outline, became visibly 

 fibrous in their structure, and gradually faded away. The advent 

 of a new colloid, differing ever so little from the first, determined a 

 complete disorganization of the attractions which held the molecules 

 together. They — the molecules — were reft asunder for a time, and 

 were afterwards gathered into new spherical combinations. In 

 applying the principle deducible from these observations to the 

 explanation of the formation of the tubular erosion-spaces in bone 

 which have been called Haversian spaces, a seeming difiiculty 

 arises. We have indeed no reason to assume that the quality of 

 the circulating and acceding colloids varies in such a way as to bring 

 about such a difl'erence between the sphere and the surrounding 

 matter as was present in the experiment. The seeming difficulty 

 rests upon the assumption" that the colloid matter entering into the 

 spherical combination remains unchanged. If we can be convinced 

 that the colloid is changed by reason of its prolonged contact with 

 the crystalloid matter, we can understand how the afllux of fresh 

 Bupphes of the original colloid may determine the breaking-up of 

 spherical combinations wherein tlic original colloid has undergone 

 chemical and physical change. It can be shown most clearly that 

 the colloid matrix of spheres, whether of collagenous or of albu- 

 minous nature, is altered after no very long time. It takes on 

 chemical reactions approaching those belonging to ripe epithelial 

 structures and chitine. Such a change, if occurring in bono, may 

 be conceived to be a part of senescence. The transformation of 

 an active into an inactive colloid must presently call for complete 

 reorganization. The altered balance of colloids will constitute an 

 enabling condition. Each part of a bone as it grows old is swept 



