198 NON-INFLAMMATORY DISEASES OF BONES. 



The case related at page 183 goes to prove that the two 

 conditions are quite distinct in the horse, as in that case there 

 was simply a removal of the earthy constituents, rendering the 

 bones flexible and easily cut with the knife. I contend this 

 is the true mollities ossium; whereas in the disease now under 

 consideration fatty material is substituted for the cartilaginous 

 basis, without removal of the earthy matter, and in this way 

 the bones are rendered brittle, and liable to fracture from 

 unappreciable causes. 



The second form of fragilitus ossium, resulting from old age, 

 can scarcely be looked upon as a disease, since it is as much 

 the natural state of the senile skeleton as the soft pliable con- 

 dition of the bones is that of adolescence. 



Bones, when affected by chronic inflammation, however, are 

 rendered exceedingly brittle and liable to fracture ; and it is 

 interesting to note the progress of ostitis leading to such a 

 condition. First of all, if the extremity of a bone be examined, 

 by making a section of it, when in the early stages of inflam- 

 mation, it will be discovered that the first change has been the 

 removal of the fat from its cancelli ; that a fibrinous exudate 

 has taken its place ; and that this deposition is being gradually 

 replaced by osseous material. After a time, the open, areolar 

 appearance of the interior of the bone assumes that of compact 

 tissue, the bone at the same time increasing in weight. This 

 condition may continue for a very indefinite period, and in some 

 cases no further change takes place, but in others open spaces 

 are formed by absorption of the new bone. These spaces are 

 small at first, but become enlarged by removal of their walls, 

 and by the coalescence of two or more oi them. Thus the solid, 

 compact bone again becomes cancellated, but this cancellated 

 structure is very different from the original; for the bony 

 trabeculse are now deficient in animal material, are mostly 

 made up of the earthy constituents of bone, and are thus brittle 

 and ready to break upon the slightest application of force. The 

 bones most liable to assume this condition are the tarsal, cunei- 

 form, navicular, and pedal bones ; and these are all composed 

 of a very thin, compact shell, and much cancellated tissue. 

 This compact layer is frequently involved in the diseased pro- 

 cess going on within, and covered with small nodules of bone ; at 

 other times it is ulcerated on its surface, or both conditions may 



