936 Eaehitis. 



Finally an insufficient assimilation of lime in the bones is 

 often supposed to be a cause of rachitis, the osteoid tissue 

 being incapable of making use of the lime salts carried there 

 in the circulation and of retaining those that have been de- 

 posited. The abnormal condition of the osteoid tissue is be- 

 lieved to be shown by the fact that the bone substance contains 

 only glutein instead of ostein. No positive proofs' have as yet 

 been afforded for the correctness of this hypothesis. 



Not infrequently the influence of predisposing factors can 

 be shown. It is commonly known that an absence of sunlight, 

 but preferably confinement in damp stables or in similar places 

 (cellars, dark, damp rooms) promotes the development of 

 rachitis; up to a certain degree a like influence may possibly 

 be attributed to insufiicient ventilation or exercise (Hansemann). 

 The possible influence of digestive disorders has already been 

 mentioned. It is also probable that there are individual differ- 

 ences in predisposition. The state of nutrition or the amount 

 of fat deposited in the tissue may insofar be of importance 

 as, other things being equal, fat animals of much greater body 

 weight become ill much sooner and also more severely. 



The influence of predisposing factors may perhaps be explained thus that 

 they affect adversely the metabolism in fee organism and indirectly the calcium 

 content there or in the bones, and that they also encourage the occurrence of an 

 intoxication or infection. It is also probable that in some species the want of 

 earthy ingesta is to be considered. 



Although a predisposing role has often been attributed to 

 heredity its influence is probably at most an indirect one. If 

 in a given herd the disease appears more frequently and in 

 several generations, the cause must, as a rule, be looked for 

 in improper conditions of maintenance, also in close inbreeding 

 or in disease of the mother animals. Under such circumstances 

 weaker and less resistant individuals are born whose metabolism 

 is easily disturbed by insignificant influences. 



For the present it still appears questionable whether Rhachitis 

 foetalis occurs in animals. Marchi made the observation that in the 

 Chiana valley in Italy the cows give, in damp years, birth to somewhat 

 smaller calves whose extremities show remarkable curvatures, the bones 

 being twisted and short, the epiphyses comparatively long, the diaphyses 

 long. Histological examinations were not made. In this valley the 

 conditions of the soil are unfavorable and the feed consists principally 

 of sour grass; since the soil has been cultivated appropriately, the 

 disease has become much less frequent. Similar observations were 

 reported by Sivieri, Hansen, and before them by Siedamgrotzky. The 

 cases are however probably instances of abnormal development 

 (Osteochondrodystrophia foetalis) (Zsehokke, Bourdelle & Dubois). 



Hardly anything is known in animals about rachitis which com- 

 mences soon after birth (rachitis congenita). Only Hansen mentions 

 a few cases of rachitis in colts which were affected when about one 

 month old. However they were all sired by the same stallion and 

 came from mares that had already had colts with congenital rachitis. 



