The common form, and that which is the usual subject of the text-books and monographs, has, however, in most cases a well-marked preparatory stage in the shape of diseases or ailments reducing sanguification {144} and nutrition. Some cases are ushered in by, or follow the course of, acute exanthems or acute gastric disorders or the presence of entozoa. A larger number appear to result from insufficient oxygenation resulting from lung diseases, with a long chronic ailment following the acute stage. Even acute pneumonia, with its direct influence on general nutrition, stands often for the proximate cause of rachitis. Bad air alone, even swamp air, does not appear to be a sufficient cause. When it seems so, it is complicated with the main cause of rachitis; that is, bad, insufficient, improper food, with its immediate result--viz. intestinal catarrh. Cow's milk, particularly when acid, starchy food administered too early or in too large quantity or too exclusively, early weaning followed by improper artificial food, insufficient mother's milk or such as is either too thin or too caseinous, lactation protracted beyond the normal limit,--may all alike be causes of intestinal disturbances and rachitis. Is rachitis hereditary? A number of women who were rachitical themselves have been known to have rachitical children. But it has been said that the process runs its full course during infancy, and that therefore a direct inheritance of rachitis from mother to child is an impossibility. Still, we must not forget that the consecutive conditions of the parents may, or will, influence the general condition of the infant and result in similar disturbances. No rule, however, exists. Dyscrasic parents may have healthy children, and healthy parents sickly or dyscrasic ones. But the probability is greater that diseased children should come from dyscrasic parents than from healthy ones. Tuberculosis in the parents has frequently been accused of being the cause of rachitis in the infant--not directly, but in consequence of general impairment of the tissues. Gout has also been accused of being the cause of rachitis, but it is a peculiar fact that the poor have but little gout and a great deal of rachitis. In all of these cases it is better to look upon rachitis as only one of the forms of general mal-nutrition, and to speak of inheritance of the disposition rather than of the disease. Thus it was that about the end of the eighteenth century Portal spoke of scrofulous, syphilitic, scorbutic, rheumatic, arthritic, and exanthematic rachitis. Particularly has syphilis been accused of being the main cause of rachitis by some, and even the only cause by others. Thus it was looked upon by Boerhaave. In modern times Parrot maintained, from 1872 up to the time of his death, which occurred recently, that every case of rachitis is of syphilitic origin. As his proof he relied mainly on the condition of the teeth and the bones.