328 ON' KENTAI. iNcur.vrATioxs 



Extended observation has satisfied me that the incrustation, in greater or less 

 degiee, is common to all mammals, and also to a number of otlier animals, in 

 every ease being of the same general character. I have found it. for instance, in 

 the crocodile (C. purosus) Queensland, killer v.hales {Orca gladiator), and in 

 one individual or another of practically every mammalian species examined. It 

 will suffice to give the names of a few as indicating the scope of the investigation: 

 Tapir, eland, American bison, hippopotamus, various bears, dog, cat, rat, mouse. 

 Examination of the skulls of marsupials in the Australian Museum collection and 

 elsewhere disclosed numerous examples: Mucropins major, cjuite as heavy as that 

 of the sheep, J/, ijiganteus, 21. riifus, Phascolarctus civereus. Phaf^colomys mit- 

 chellij Da.si/tire, and many others. The original observations of Dr. Bennett are 

 thus completely confirmed. Fossil marsupial teeth from Wellington Caves, Xew 

 South Wales, in the Australian iluseum, still ha^e adhering brown patches which 

 I take to be the same deposit. Where\"er the teeth of animals were noticed to 

 have a yellow or brownish tint as in aged rats, minute examination showed this to 

 be due to the same cause. 



In response to queries from me, Mr. Brov.n has supplied me with the follmv- 

 ing very interesting notes: — '"Tartar fonns on artificial plates, especially lower 

 plates, quite as readily as on the natural teeth; it is an everyday occurrence to 

 see that. It is deposited along the lower portion of the lingual side of the plate, 

 and dentists are continually asked by patients what it is and how to remove it. 

 I do not remember seeing teeth forming jjart of a Ijridge witli tartar deposited on 

 them, but frequently find that the gum having slightly receded after the bridge has 

 been fixed; a slight deposit is to be seen round the gingival margin of the natural 

 roots to which the bridge is attached. Porcelain crowns (pivots) and gold 

 crowns or caps remain free from deposit. I once had to remove from an elderly 

 woman's mouth a little lower plate having three teeth on it, and there was such 

 an accumulation of tartar all about the whole structure and the remaining teeth 

 that two of the latter were extracted in the removal of tlie plate; these. ho\vevc>r. 

 were loose from pyorrhoea. In this case the tartar had certainly eiu-roached to 

 some extent on the artificial teeth. The iiatient informed me that she had not 

 removed the denture since the dentist luit it in place many yeai-s before. This 

 case was an exceptional one, and as I have mentioned. T do nut remember seeing 

 deposit on artificial teeth at any other tinu\" 



I think it is proliable tliat the nature of the surface of ixircelain teeth and 

 gold crowns inhibits the adliesion of deposit. In the case of the urinary tract, it 

 is well known that any solid foreign body, such as a piece of broken catheter, 

 soon becomes coated with phosphate, and that a little blood clot or even bacteria 

 mav foim the nucleus of a urinarv calculus. 



