170 MICROSCOPIC ANATOMY OF THE TEETH 



These observations perhaps afford a clearer insight into 

 the actual method by which calcium phosphate comes to 

 predominate in teeth and bone than any that have been 

 hitherto presented, and if fully confirmed will remove many 

 difficulties in the clear comprehension of the actual physical 

 and chemical processes in calcification. 



A very interesting research has been recently undertaken by Mrs. E. Mel- 

 lanby, the first results of which are embodied in a paper published in the 

 Lancet on December 7, 1918. These experiments were undertaken to 

 throw additional light on the influence of diet on tooth formation, and 

 were carried out on the teeth of puppies. It would appear that the 

 incorporation of the proper amount of calcium salts with the teeth is 

 dependent not so much on the amount of calcium in the diet as on the 

 action of some determining factor in the food which is the cause of the 

 efficient allocation of calcium salts to the forming teeth. This determining 

 factor would appear to be, in the author's words, ' a diet containing an 

 abundance of those articles with which the fat soluble A accessory food 

 factor is associated, e.g. cod-liver oil, butter, &c.', allowing ' the develop- 

 ment in puppies of :.ound teeth '. A diet otherwise adequate, but deficient 

 in the substances with which fat soluble A is associated, brings about 

 defects in puppies' teeth. These effects are described as delay in the loss 

 of the deciduous and eruption of the permanent teeth, and defective 

 conditions of the enamel. The calcium may be present in the food in such 

 a form that it can be easily taken up by the blood, but if this accessory food 

 factor is absent, the cells of the formative organs of the teeth are unable 

 to perform their calcium-separating functions with success * owing to the 

 lack of one or more factors in the blood-stream which normally regulate 

 this function '. The further record of the results of these experiments will 

 be awaited with much interest. 



Summary It is generally considered that the calcification of enamel 

 is brought about by a process of secretion from the cells 

 of the enamel organ, and not, as stated in former times, 

 by an actual conversion of the substance of the cell into 

 enamel. 



The Tomes' processes of the ameloblasts, however, do 

 become incorporated in the formed enamel. 



Blood-vessels are not usually seen in the enamel organ 

 of mammalia, but vestiges of these are found in the external 

 epithelium and in the stellate reticulum of some marsupials, 

 and are described by Leon Williams in the stratum inter- 

 medium in the later stages of calcification in the rat. In 

 the enamel organs of some fish, however, blood-vessels are 



