Pathogenesis, Anatomical Changes. 



955 



the affected animals, the more so, as both diseases may occur simul- 

 taneously. According to this viewpoint rachitis and osteomalacia would 

 form processes which are identical anatomically, but which might 

 possibly be due to different causes. But since many points are still 

 disputed concerning the etiology and pathogenesis of both disease forms, 

 the identification of rachitis and osteomalacia as one clinical entity of 

 like anatomy and etiology does not appear justified for the present. 



The relation of rac-hitis and osteomalacia to osteoiiorosis in ge^^eral ( rarifica- 

 tion of bony substance in favor of the marrow spaces) may be described as 

 follows: Both in rachitis and in osteomalacia osteoporosis is a constant symptom, 

 and it is either emphasized very slightly compared with the proliferative process, 



Fig. 166. Pelvis of a oow ivith osieomalacia. The pubes and iscliiuni are bent, 

 the foramen obturatum being distorted. The left internal angle of the ilium is 

 lowered. 



dependent upon the age of the affected animal, on the cause and on the variable 

 mechanical influences, or on the contrary it predominates, at times so decidedly 

 that it appears to exist alone. It is therefore not proper, at the present stage of 

 information, to classify general osteoporosis (with the exception of senile bony 

 atrophy) as an indepjendent affection apart from rachitis or osteomalacia, as was 

 recently proposed by Miwa & Stoltzner, Elliot, Theiler and others. 



Anatomical Changes. In well marked cases of the disease 

 the marrow spaces of the lon.n' l)ones are dilated, the bony 

 cortex is thin and spongy, brittle, or then so soft that it may 

 he cut with a knife. In very severe cases the cortical portion 

 of the long bones is barely a few millimeters thick, the bone 



