April 21, 192 1] 



NATURE 



249 



Gold-coloured Teeth of Sheep. 



I 



'N a paper " On Dental Encrustations and the So- 

 called ' Gold-plating ' of Sheep's Teeth," pub- 

 lished in the Proceedings of the Linnean Society of 

 New South Wales (August 25, 1920), Mr. Thos. Steel 

 gives an account of the so-called "gold-plating" and 

 encrustations on the teeth of sheep and other animals. 

 He states that the popular idea is so strong that the 

 jaws of sheep are still taken from time to time to the 

 Sydney Mint with the object of selling them for the 

 gold supposed to be present. 



Mr. Steel refers to papers published in the Pro- 

 ceedings of the Royal Society of New South Wales 

 and of the Sydney Section of the Society of Chemical 

 Industry in 1905, in which Prof. Liversidge showed 

 that the encrustation is due to tartar deposited from 

 the saliva in thin films. The golden colour and 

 appearance are proved to be due to the reflection of 

 light from the overlapping of the thin films, and in 

 composition the deposit consists of impure calcium 

 phosphate and organic matter, and not of iron pyrites, 

 as confidently asserted by correspondents in Nature 

 (vol. xcix., 1917, pp. 264, 284, 290, and 306, and vol.c, 

 1917, p. 106), to account for which various "fantastic" 

 explanations are given. Prof. Liversidge stated that 

 the deposit can be easily separated in thin flakes 

 like mica with the point of a penknife, or even' a pin, 

 and that if a flake held on the point of a pin be placed 

 in a match- or candle-flame it blackens, inflames, and 

 leaves a white fusible residue; hence neither a know- 

 ledge of chemistry nor the use of any chemical ap- 

 paratus is necessary to prove the absence of gold and 

 of iron pyrites. 



Mr. Steel has unearthed a forgotten statement by 

 the late Dr. George Bennett in his " Wanderings of a 

 Naturalist" (1834, p. 294) that the yellow "metallic 

 substance " sometimes f6und on the teeth of sheep, 

 oxen, and kangaroos, and frequently mistaken for 

 gold, is simply tartar deposited from the saliva. Dr. 

 Bennett quotes an analvsis of the ordinary deposit 

 on human teeth by Berzelius, who obtained results 

 verv similar to those of Mr. Steel. Mr. Steel had 

 exceptional opportunities for obtaining large quantities 

 of the coating, and was able to make quantitative 

 analyses of the encrustations from the teeth of sheep, 

 oxen, horses, etc., taken from the stocks of bones 



passing through a large bone-charroal factory in 

 Sydney ; from other sources he obtained sufficient 

 material from the teeth of the camel, dromedary, 

 rhinoceros, and even man. They consist mainly of 

 calcium phosphate, with small amounts of magnesia, 

 carbon dioxide, a little sand, from 16-20 per cent, to 

 2465 per cent, of organic matter, and from 385 per 

 cent, to 11-65 P6^ cent, of water. Mr. Steel g^ives a 

 table of the percentage composition of the encrustation 

 from the teeth of man, sheep, ox, camel, dromedary, 

 and rhinoceros and, for comparison, the analyses 

 of the cement layer (crusta petrosa) of the teeth of 

 the babirussa, ox, and camel. He points out the 

 very interesting fact that the tartar has much the 

 same composition as( mammalian bone. 



The rhinoceros and babirussa encrustations differ 

 from the others by containing- very little calcium 

 phosphate, although in lustrous flakes like that of 

 the sheep and ox; in man it is chalky-looking with- 

 out the metallic or nacreous lustre. 



The coating may vary from a thin film to a quarter 

 of an inch in thickness ; the black coating common 

 on the teeth of sheep and oxen has the same com- 

 position as the "metallic" deposits. The teeth of 

 carnivora and rodents are usually very clean except 

 when old, and so are those of pigs ; those of snakes, 

 lizards, and fish are free from deposit ; it is present 

 on the teeth of the crocodile and killer-whale, and 

 also on teeth of the tapir, eland, bison, bears, 

 and most of the Australian marsupials, including the 

 fossil marsupial teeth from the Wellington Cave, New 

 South Wales. Mr. Steel refers to the huge projecting 

 teeth observed by Miklouho-Maclay in natives of Taui 

 or Admiralty Islands (N.ature, vol', xvi., 1877, P- 251), 

 due to an enormous deposit of tartar caused by 

 chewing- betel-nut and lime ; the percentage of lime 

 found in it by Salkowski was more than 45 per cent. 

 (Nehr. Berlin. Ges. Anthrop., 1881, p. 219). 



The investigation shows a large amount of very 

 careful and painstaking work, and should be of 

 interest to anatomists and dentists, especiallv as the 

 alleged occurrence of gold or pyrites on teeth "has been 

 reported again and again for centuries, and will 

 probably continue to be so reported from time to 

 time. 



The History of Metamorphic Insects. 



REFERENCE has been made in Nature to most of 

 the series of remarkable entomological papers 

 which Dr. R. J. Tillyard has communicated during 

 the last few years to the Linnean Society of New 

 South Wales, and which have been published in that 

 society's Proceedings (vols, xli.-xliv.). These papers 

 are worthy of the most careful attention of students 

 of insects, because the author combines the power of 

 intensive research into details of structure with a true 

 ~ instinct for those details that are of real importance 

 in the elucidation of relationships, and with a broad 

 morphological outlook on the group under considera- 

 tion. He has the faith — which many of our younger 

 naturalists, shut in to the study of the inheritance of 

 varietal and specific characters, lack — that a know- 

 ledge of the phylogeny of large systematic groups is 

 attainable, but he realises that such knowledge can 

 come only through a careful comparison of recent 

 adult and immature with extinct forms. Thus his 

 evolutionary speculations are raised on surer founda- 

 tions than those which content^ many of his pre- 

 decessors. 



NO. 2686, VOL. 107] 



Attention may be especiallv directed to Dr. Till- 

 yard 's exposition of the wing- venation of the group 

 of orders which he terms the " Panorpoid complex" 

 (Proc. Linn. Soc, N.S.W., vol. xliv., part 3, 1919), this 

 group comprising the Neuroptera (Planipennia and 

 Megaloptera), Mecoptera, Trichoptera, Lepidoptera, 

 and Diptera, together with three extinct (Permian or 

 Triassic) orders, the Paramecoptera, Protomecoptera, 

 and Paratrichoptera, the types of which were described 

 by the author from Australian fossils. W^ing-venation 

 has been generally regarded as a trustworthy guide to 

 the affinities of the families and orders of insects, but 

 entomologists lacked a reasonable morphological inter- 

 pretation of the complicated array of facts until Com- 

 stock and Needham showed how the correspondence 

 of the main series of longitudinal nervures could be 

 traced through members of various orders, the detec- 

 tion of homologies being greatly facilitated by a study 

 of the tracheal tubes which provisionally mark out the 

 venation in the nymphal or pupal wing. Dr. Tillyard 

 adopts generally the Comstock homologies and nomen- 

 clature, but his opportunities of studying archaic 



