BV T. .STEEL. 



327 



Lime ■^S • 



Pliospboric oxide 3l) . 



Oi"auie matter anil wattT -l- 



100. 



These figures agree very well with my analysis of the liumau prodiu-t. In 

 my examination 1 found the total loss on ignition, including water and carbon 

 dioxide, was 24 % and the ash 76 %. 



In my analysis, in every case the sand was m the form of mechanically em- 

 bedded grains. It will be noticed that the incrustations from the Rhinoceros and 

 Babirussa (a pig-like animal from N. Celebes) differ from the others in contain- 

 ing but little phosjihoric acid and a considerable proportion of calcic carbonate. 

 In both of these the scale, w-hen detached, was in appearance much like that from 

 the sheep and ox, being in clean shining flakes. In man it is chalky-looking and 

 has not got the metallic, or more commonly, nacreous look of that from the sheep. 

 The similarity in comiiosition between most of the incrustations and that of the 

 cement layers of ox an<l camel is striking. Ordinary maunualian lione has also 

 a very similar composition.* 



In making the analyses, care was taken in separating lime an<l magnesia, by 

 double precipitation of the lime in the cold to avoid co-precipitation of magnesia. 

 The proportions of lime and phosphoric acid present are such as to indicate 

 that the phosphate of lime does not exist entirely as the tribasic (Cas P2 O.s). but 

 that a variable amount of the tetrabasic (Cai P2 On) is also present. I have 

 found. this to be a usual condition in many natural phosphates sucli as those from 

 Ocean Island. 



Bearing in mind the analogy between these dental salivary incrustations and 

 urinary calculi, a careful examination was made of those from man, sheep and ox 

 for oxalic and uric acids, but with entirely negative results. 



I have examined the deposit from a large variety of animals in addition to 

 those already mentioned, using micro-chemical methods when the amount available 

 was minute, and in every case have found it to be of substantially the same nature. 

 The quantitx- present varies from a mere trace of brown film, to a heavy incrusta- 

 tion packed round the crowns of the teeth and forming a continuous coating along 

 the sides as much as a quarter of an inch in thickness. It is heaviest in herbivorous 

 animals and in man. The teeth of the carnivorae and rodents are usually very 

 clean ; this is well seen in dog-s, cats, mice and rats, though all of tiiese. particu- 

 larly when old. and also rabbits, frequently have a thin brown film even on the 

 incisors. Some individuals are more predisposed to dental incrustation than 

 others. This is well-known in man, and T have noticed it in sheep and other 

 animals. The teeth of snakes, lizards and fish in so far as I have noticed, ap- 

 ))ear to be always quite free from deposit. 



I do not think that the nature of the pasture, as has sometimes been asserted, 

 has anything particular to do with the abundance or otherwise of the deposit on 

 sheep's teeth, but tliat it is purely a physiological idiosyncrasy. Sheep and oxen 

 very commonly have the teeth coated with a uniform, thin, dead black film, but 

 this does not differ in composition from the thicker deposit. The common pig 

 has very clean teeth . I have examined many hundreds of pigs' jaws, and have 

 never noticed more than traces of a brown film. 



'Watt's Diet. Chem.,.vi., 1879, 1st. Supp., .357. 



