Etiology. 937 



In a large herd of cattle in which many of the cows were affected with 

 osteomalacia, only poorly developed calves w^ere born with very delicate 

 bony structures, which however presented no rachitis symptoms; these 

 symptoms appeared only after the calves were weaned and when they 

 received similar food as the cows (authors' observation). 



From what lias been said it is above all evident that the 

 etiology of rachitis cannot by any means be said to be com- 

 pletely explained. This much may be asserted that the same 

 factors do not always participate in its development and that 

 therefore the disease does not represent an affection of uni- 

 form etiology. There is no doubt that in domestic animals 

 the most frequent cause of rachitis lies in the deficiency of 

 lime in the organism from whatever cause, no matter whether 

 the disease is sporadic or epizootic. Whether the lime deficiency 

 causes the bony changes immediately or perhaps only creates 

 a foundation on which the rachitis develops through the inter- 

 mediation of a resulting disturbance in metabolism cannot for 

 the present be decided definitely. On the other hand a toxic 

 or infectious origin cannot be denied for certain cases, especially 

 for those with excessive proliferation of the osteoid tissue, but 

 the investigations which have been undertaken in this respect 

 are not yet sufficient to justify a definite position being taken 

 in this problem. 



Pathogenesis. If a deficiency in calcium occurs in the 

 organism the calcification of the developing osteoid tissue re- 

 mains insufficient and this leads to a lessened firmness of the 

 bones. The more the firmness of the bones diminishes, the 

 greater is the mechanical irritation exerted upon the bone- 

 forming tissues by the motion of the body or of parts of the 

 body, and by the coincident jolts and shocks. In consequence 

 there occurs an increased new-formation of osteoid tissue with 

 proliferation of the epiph3^seal cartilage and bone marrow 

 tissue, that is, a process similar to a productive inflammation. 

 The severity of the mechanical irritation depends not only 

 on the degree of lime deficiency but also on the body w^eight 

 of the animal, and especially upon whether, and in what degree, 

 the animal is permitted to move about or does move about of 

 its owm accord. As a consequence of the lime deficiency in 

 the organism there occurs a partial or even a complete cessa- 

 tion in the ossification of osteoid tissue, through which the 

 solidity of the bones becomes less and less in spite of the in- 

 creased function of the bone-forming tissue. It is as a further 

 consequence of the lime deficiency, that we may consider the 

 abnormally increased absorption of bone tissue wdiich had been 

 formed before the disease (osteoporosis). 



Although the disturbances in the bone formation occur in 

 various parts throughout the body, they reach a considerable 

 degree only in certain parts under the influence of the con- 

 stantly changing mechanical irritation. 



