A deficiency of earthy salts in the food has been a natural and favorite explanation, and the ill-health that is thereby brought about is often an important factor. Yet rachitis occurs independently of such a condition.
In Roloff’s experiments, pigs fed on aliment deficient in lime salts, suffered from bone softening, while the control animals on food rich in lime salts remained well. The diseased animals further recovered on a diet rich in lime. Voight, Chossat, Milne-Edwards, Lehmann, Bousaingault, Heitzmann, etc., had similar experimental results, and the effects were shown in goats, sheep and dogs, in curvature, shortening, swelling of the costal cartilages and joints and contracted pelvis. Growing pigs have often been found to suffer in this way when placed on an exclusive diet of maize. The great improvement often secured in feeding an excess of calcareous phosphates tends to corroborate the hypothesis. Wagner found that food rich in lime salts, and the administration of small doses of phosphorus, rendered the epiphyses of the growing bones more compact. Kassowitz, on the other hand, found that an excess of phosphorus caused absorption from the bone substance and an irritable inflammation of the osseous tissue. Schneidemühl has seen the disease in calves raised on milk, poor in lime, the product of emaciated cows; in pigs getting only potatoes and swill, and in puppies that were denied bones. It is common in pigs on an exclusive diet of maize. Yet it is most destructive in many breeding studs where the alimentation is rich and generous. It must be admitted that as a concurrent cause, the paucity of lime salts and phosphates is a powerful factor, and that in supplying the bone ash, and improving the nutrition, these often prove of great value. Their privation is, however, not an essential condition of rachitis.
Free phosphorus. Ziegler and Kassowitz emphasize the hyperæmia of the cancellated tissue, and Wagner shows that this condition can be induced by excess of phosphorus, but this excess of phosphorus has not been found in the blood in ordinary cases, and is not likely to occur in a great number of young, at the same place and time, irrespective of food, as has been shown in breeding studs in New Jersey, in the South and West. In particular cases excess of phosphorus may operate, but it cannot be looked on as universal or essential.
The presence of glycero-phosphoric acid is alleged by Trasbot, but there is no proof of its constancy in rachitis, nor would its presence explain the real cause of the disease.
Lactic acid in the system. Lactic acid, in vitro, dissolves the calcareous salts of the bones. Trasbot alleges that it opposes the precipitation of lime in the form of tribasic phosphate, as found in bone. Siedamgrotzky and Hofmeister found that the salts of the bone were lessened under the administration of lactic acid. Heitzmann and Baginsky showed that by restricting the lime in food and giving lactic acid, by the mouth or subcutem, the lime salts in the bone were lessened relatively to the organic basis. It should be noted that an exclusive diet of buttermilk is liable to cause an attack of arthritic rheumatism. Lactic acid is undoubtedly a coöperative factor in certain cases, but though often found in the diseased bone and urine of rachitic children (Ragsky, Morehead, Simon, Lehmann), it is not shown to be constant.
Oxalic acid. Acetic acid. Formic acid. Beneke found oxalic acid in the urine in many cases of rachitis and attributed to it the removal of the lime salts. Others have made the same charges on acetic and formic acids which are sometimes found in the diseased bone.
It is quite plain that the process of normal ossification is easily disturbed, and that the same agent (lime, phosphorus) will assist or hinder according as it is present in small or large amount, and that certain chemical agents like organic acids may act injuriously even in the presence of an abundance of bone salts.
Heredity. Rickety parents have often rickety offspring, the weak somatic cells, failing in both cases to build healthy, strong tissues, but as a rule also, both have been condemned to live in similar unwholesome surroundings.
Unhygienic Conditions. Schneidemühl notes that in animals as in man, bad ventilation, close impure air, crowding, damp impervious soils, and cold, are found more or less in places where rachitis prevails. By lowering the general health and tone, these debilitate the tissue cells and impair nutrition and growth.
Confinement has a manifest influence. Rickets prevails in children in the great manufacturing cities, where the exclusion of sunlight and the breathing of impure air rob the system of its vigor. The children of soldiers in India kept in close barracks are largely rickety, while the more poorly fed native children outside escape. Wild beasts in confinement are often rachitic, unlike their fellows of the forest. Colts in confined stables suffer while those in the fields and yards remain healthy. Swine in Sweden in close pens and fed on potatoes alone suffer (Stockfleth).