OSTEO-POKOSIS. 197 



the absence of some essential ingredient of the food, or its pre- 

 sence in such small quantities as to te insufficient for the 

 necessities of the animal ; or the presence of some other con- 

 stituent of the food m such super-abundance as to destroy the 

 pptfect composition of the aliment as a whole, and thus render 

 It unfit for assimilation by, or so change it aa to cause it to become 

 even an irritant to, the osseous system of the animal. 



PRAGILITUS OSSIUM. 



Fragility of hones results from two pathological conditions, 

 namely — lei. Fatty degeneration of the animal basis ; and 2d. 

 The presence of an undue quantity of earthy materials, due to 

 old age or to ostitis. 



Tlie ?rst form is a constitutional disease, with no sjonptoms 

 indicative of its presence during life, discovered only after a 

 fracture of such a nature as to be incurable, and when the animal 

 is exanyned after death. — (See Photo- lithograph, Plate I., Fig. 

 3 ,) I have, howevet', observed that narrow-loined horses are liable 

 to this disease — bad thrivers, as they are called — with small 

 articvJations, badly-formed hocks and knees, round pasterns, 

 &c., and having a tendency to fall lame from bone-spavins, ring- 

 bones, or other osseous diseases. As a rule, they are middle- 

 aged horses, and the posi mortem examination shows the bones 

 — more especially the pelvic and vertebral — in a peculiar greasy 

 condition, yellowish in colour throughout their substance, and 

 with their cancelli filled with a dirty yellowish fat. When 

 microscopically examined, the minute structure of the bone is 

 found to be filled with fat globules ; in fact, their structure 

 is not only infiltrated, but partly composed of fat, traversed, as i^ 

 ;syere, by the natural bony material. 



Writers upon surgery describe fatty degeneration of bone 

 Tender the head of mollities ossium, or softening of the bones; 

 indeed, there seems to be a confusion amongst them on 

 this subject, some giving the pathological anatomy of osteo- 

 porosis, others of fatty degeneration. Paget, however, says 

 that two diceases are described as mollities ossium, namely 

 fatty degeneration, and the simpler softening of bone, or osteo- 

 malacia rhachitismvis adultorum, in which the bones are flexible 

 rather than brittle. 



