The assimilation of the Steenbock-Black diet in normal and vitamin-D deficient rats with and without caecum

THE rat, like other species, needs vitamin D for optimum health.It is generally accepted, however, that the vitamin is not necessary for the prevention of rickets in rats, provided that the diet is furnished with a well balanced Ca/P ratio; provided also that these two elements are present in the diet in a readily available form.The lessened susceptibility of the rat to rickets compared with other species, even in absence of vitamin D, has been explained by the considerable ability of this animal to absorb ingested Ca and P [Harris, 1932].Its cause has, however, never been investigated experimentally.In the rachitogenic rations most generally used in experiments on rats, cereals, such as maize and oats, form a regular and essential component of the diet.In the Steenbock-Black diet 76 parts are yellow corn.Both in maize and oats the essential source of P is phytin (inositolhexaphosphoric acid).The significance of this form of P in the patho- genesis of rickets has been emphasized by Bruce & Callow [1934].Phytin is not attacked by any enzyme secreted in the digestive tract.The utilization of P from this source is therefore limited to the amount which can be split off by bacterial action.Now it is well known that parts of the ingested food may be recovered from the caecum of rabbits more than a week after the ingestion.During preliminary studies of the passage of the intestinal content through the digestive tract of the rat, a similar stagnation of ingested food was observed in the rat's caecum.Carmine ingested with the food was found to stain the content of the caecum bright red several days after ingestion.In rats starved for 24 hours the caecum is full, whereas the rest of the gut is nearly empty.This stagnation of the remnants of ingested food in the caecum will favour any bacterial action.It seemed possible therefore that the utilization of the phytin P might be favoured by this action, which would explain the better ability of the rat to