The time of weaning is often a starting-point for rickets, for the breast milk is usually replaced by some preparation of starch. So also long continued suckling may induce the disease, for the breast-milk after a time ceases to satisfy the infant's wants, and too little additional nourish ment is supplied. Therefore whether the food given be insufficient in amount or indigestible in form the effect is the same : the child is starved and rickets becomes developed.
In cases where the child lives in a good 'gracing air the effects of an un suitable dietary are less painfully evident. In dry country places, where the infant spends much of his time out of doors, rickets is a more uncom mon disease than it is in localities where the conditions are less favourable to health. Want of sunlight, want of cleanliness, and a combination of cold and damp are other determining causes which are not without their influence in the production of rickets. All these causes must no doubt act with especial energy in the case of infants who are naturally weakly, or whose strength has been already reduced by some exhausting disease. There are, therefore, many conditions which predispose to the complaint. Feebleness of constitution on the part of the parents will, no doubt, have an influence in this respect, for weakly parents are not likely to beget con stitutionally healthy children. Moreover, a weakly mother is usually unable to nurse her baby ; and hand-feeding, unless conducted with extreme care and discretion, is often unsatisfactory. A very large proportion of rickety infants are bottle-fed.
Hereditary tendency is considered by some observers to be an element in the etiology of the disease. In the case of so common an affection it must no doubt often happen that the father or mother of the patient has been previously affected in a similar way ; but that a parent who had been rickety in childhood should give birth to a weakly infant, and that this in fan+, brought up in violation of all the rules of health, should develope rickets, is surely but slender evidence in favour of the hereditary trans mission of the disease. Supporters of this theory, usually point to the cases of so-called "congenital rickets" as instances of the inherited form of the disease ; but, as is hereafter explained, there are reasons for exclud ing these cases from the class of true rickets.
The relation which exists between rickets and congenital syphilis has within the last few years been brought into great prominence. M. Parrot
has laboured to show that rickets is always the consequence of an heredi tary syphilitic taint. The arguments of this observer in favour of his view are derived chiefly from morbid anatomy. He points in particiflar to the anatomical changes observable in the epiphyseal ends of the long bones in the two diseases as evidence of the specific nature of rickets. But the latter is not only a disease of the bones ; and although the epiphyses in the two cases may present a certain similarity of lesion, there are other alterations of structure in rickets which are different from those of syphilis. Moreover, the general symptoms, especially the peculiar tendency to functional ner vous disorders, have no counterpart in the specific disease. Again, rickets is constantly met with in cases where the most careful inquiry and most minute examination fail to detect any history of venereal taint in the parents or sign of it in their offspring. The disease is common in localities where congenital syphilis is rare, and rare in places where the latter is common. It is met with in animals as well as the human subject, and is produced in them by faulty hygiene and bad feeding as it is in the child. But it is needless to multiply arguments against the untenable hypothesis advanced by this distinguished pathologist.
Still, although it cannot be allowed that rickets is caused by syphilis, syphilitic infants may become rickety ; and it is probable that a parent weakened by a former syphilis may, without transmitting the taint to his offspring; beget a child of feeble constitution in whom rickets can be easily induced. But in both these cases injudicious feeding and insanitary con ditions must come into operation before the disease can occur.
A pronounced tubercular disposition appears to have a protective power against rickets ; for although weakly, phthisical parents may give birth to feeble infants who readily fall victims to rickets, it is rare to find the lat ter disease in a family where other members have died of tubercular men ingitis or other form of pure tuberculosis—unless, indeed, the tubercular mischief has occurred secondarily to rickets. The reason of this immunity seems to be that the causes which are capable of setting up rickets will in duce tuberculosis in child predisposed to this form of illness and very quickly bring his life to a close.