The exact aetiology of rickets is still unsettled, but certain factors in its production have been determined. We are not concerned here with all the causes, but there is a consensus of opinion as to the importance of the diet. As Dr. Cheadle well expresses it; "The only constant factor, always present, is the food factor. Sometimes it is the only factor. The chief cause, this fault of diet, is the commonest, the most potent, and dominant of all." An amount of clinical evidence has now been collected on this subject which is perfectly conclusive. The well-known experiments of Mr. Bland Sutton at the Zoo showed that the lower animals might suffer from rickets from exactly the same causes as infants. Artificial feeding for the young lion whelps had to be employed owing to the failure of their mother's milk supply. They were fed solely on the flesh of old horses, almost entirely destitute of fat, with some goats' flesh occasionally. On this they became extremely rickety and one died. Mr. Bland Sutton then continued the meat diet, but added to it milk, cod-liver oil, and pounded bones. The change which followed was remarkable, for in three months the animals had lost all signs of rickets, and they grew up perfectly healthy. In the present day one does not usually find that it is the quantity of food which is at fault in cases of rickets, but the quality. There will be found in the previous diet an absence of certain food materials and an excessive amount of others. Expressed otherwise, there is an error of defect as regards the fatty elements - a constant factor; and an error of excess as regards the carbo-hydrate elements - a variable factor. Further analysis shows that the primary factor in the production of the pure clinical picture of rickets is a deficient amount of fat in the diet. If in addition the protein element is defective, there will be added weakness and impairment of nutrition. If in addition the carbo-hydrate element is in excess, there is apt to be gastro-intestinal disorder, followed by toxaemia from the absorption of improperly digested food or the products of the decomposition of the food.

The development of rickets takes place slowly as the result of the prolonged use of an improper diet. The beginnings of the disease are not readily recognized by the public. In certain classes of society rickets is so common that its leading features have come almost to be regarded as physiological in infants, and some rachitic babies are viewed as types of health and beauty. The disease frequently arises from the prolonged use of a food or a diet which had been ordered for some passing disorder. The food factors in the production of rickets will vary in different countries just as the feeding of infants does, but the general principles given above will hold good everywhere. In connexion with the subject of diet we shall have to consider both the preventive and the curative treatment.

The Preventive Treatment

The special preventive treatment of rickets lies in the adoption of and persistence in a proper diet. This has already been fully discussed in connexion with the feeding of infants. Custom, cheapness, advertisements, etc., have brought into common use many articles of food which are not suitable for infants, and which induce rickets when exclusively used.

The various forms of condensed milk, when diluted for use, are notoriously deficient in fat, and many of them contain an excess of sugar. This deficiency of cream is present in the best condensed milk, which is made from the whole milk, and is therefore much more marked in that made from separated or skimmed milk. There are other defects in connexion with condensed milk, which render it unsuitable as a complete food for infants, but only its influence in inducing rickets need be considered here. The chemical analysis which is often attached to the various brands of condensed milk is misleading, because it shows the composition of the milk when condensed, and not its composition when diluted for an infant's use. Huchison quotes from Pear-main and Moore the following analysis of some of the best brands of condensed milk when diluted as recommended for the use of infants.

Dilution recommended for Infants' use.

Fat in such product.

A.......

1 to 5

1*8 per cent.

B.......

1 „ 14

0.7

C........

1 „ 14

0.6

D.......

1 „ 15

0.7

E.......

1 " 14

0.8

F.......

1 „ 14

0.7

G.......

1 „ 14

0.7

Human milk

-

35

Both clinical experience and chemical analysis show that condensed milk from its deficiency in fat should not be used as the diet for an infant if rickets is to be prevented. Another factor in the production of rickets is the excessive amount of sugar which is present in many condensed milks. This makes a baby fat but not healthy, and is frequently the cause of gastrointestinal indigestion. In all cases in which indigestion is present any tendency to rickets which arises from the nature of the diet will be much increased. Rickets will also be developed on other forms of milk in which the fatty element is deficient, such as separated milk, skimmed milk, and buttermilk. These also stand condemned as a complete diet for infants.

The tinned starchy foods, whether converted or unconverted, are largely responsible for the production of rickets. They are characterized by a deficiency in fat and protein, and by an excess of carbo-hydrate material. In those in which the starch is unconverted there is the additional drawback that gastro-intestinal disturbance will probably be induced at an early stage, and the nutritive value of the food will be still further diminished. These "infants' foods" make fat, flabby children, but the fat is of an unhealthy character, and is quite different from the product of a diet rich in animal fat. The physiological needs of infants would be better met by a diminution in the use of "infants' foods," which might be prohibited entirely without any loss to the infantile population. If their use for infants under twelve months of age were allowed only under medical advice there would probably be a great fall in the infantile mortality from rickets in large cities. Other starchy foods, not of a proprietary nature, such as ground barley, arrowroot, and cornflour are equally effective in the production of rickets, but they have rather fallen into disuse in the present day, having been replaced by the " infants' foods".