ENAMEL 49 



tissue, was weighed and treated with dilute hydrochloric 

 acid on a water bath and evaporated to dryness. To ensure 

 the complete decomposition of the carbonates this process 

 was repeated with concentrated hydrochloric acid. Frank- Frank- 

 land's method of detecting the presence of organic matter method, 

 in the residue was adopted. ' The residue is strongly heated 

 in vacua with copper oxide, and the resulting gas, consisting 

 of carbon dioxide and nitrogen, is collected and analysed. 

 From the amount of gas formed, the amount of carbon 

 in the organic matter can be deduced, and some idea of the 

 relative quantity of organic matter can also be obtained by 

 comparison of the amounts of carbon and nitrogen.' This 

 method, Dr. Lovatt Evans states, is sufficiently delicate 

 'to detect 0-0003 gramme of carbon in 3 grammes of the 

 enamel, i.e. 0-01 per cent, of carbon, or say 0-02 per cent, 

 of organic matter, if we assume that the organic matter 

 contains 50 per cent, of carbon'. The results gave an 

 organic content of 1 to 2 per cent. 



We see that the two methods employed by these investi- 

 gators gave different results, although both agree in showing 

 that there is less organic matter present than the older 

 analyses yielded. 



It seems very difficult, however, for other reasons, to 

 imagine with C. S. Tomes that enamel is a totally inorganic 

 tissue, but the 1 to 2 per cent, of organic matter found by 

 Dr. Lovatt Evans may be quite sufficient to account for 

 the histological evidences of the presence of organic matter 

 in enamel. 



Owing to its great density and the serious interference Structure 

 with the images it presents, caused by refraction, enamel enamel!" 1 

 is one of the most difficult substances for microscopical 

 examination. The actual structure is so veiled by the dense 

 calcification, and the course of the constituent prisms is so 

 varied and complicated, that without studying the process 

 of its development it would be impossible to arrive at any 

 certain knowledge of its true histological nature. These 

 difficulties of investigation have been the cause of the many 

 contradictory statements concerning its actual structure 

 that have appeared in the various publications on the 

 histology of enamel. 



