328 Piotjal Sacielij, 



known by the name of Botany-bay resin, or yellow gum ; and finds 

 its formula to be C^(, H^g 0,o, showing that it contains more oxygen 

 than any other resinous substance hitherto analyzed. 



The general conclusions drawn by the author from these researches 

 are the following. 



1. Many of the resins may be represented by formulse exhibiting 

 their elementary constitution, and the weight of their equivalents, 

 in which 40 C is a constant quantity. 



2. There appear to be groups, in which the equivalents, both of 

 carbon and the hydrogen, are constant, the oxygen only varying ; 

 and others, in which the hydrogen alone varies, the two other ele- 

 ments being constant. 



In the third part of the same series of investigations, the author 

 examines the constitution of the resin of Sandarach of commerce, 

 which he finds to consist of three different kinds of resin, all of 

 which possess acid properties. In like manner he finds that the 

 resin of the Pinus ahie<>, or spruce fir, commonly called Thus, or or- 

 dinary Frankincense, consists of two acid resins ; the one easily so- 

 luble in alcohol, the other sparingly soluble in that menstruum. The 

 gum resin olibanum, of commerce, was found to consist of a mix- 

 ture of at least two gum resins, the resinous ingredient of each of 

 which differs from that of the other in composition and properties. 



7. " On the Markings of the Eel-back Dun variety of the Hcrse, 

 common in Scotland ;" in a letter to P. M. Roget, M.D., Sec. R.S. 

 By W. Macdonald, M.D., Fellow of the Royal College of Physicians 

 of Edinburgh, F.ll.S. Ed., F.L.S., &e. Communicated by Dr. 

 Roget. 



The author states some observations which be has made on the 

 coloured marks apparent in a variety of the horse, common in Scot- 

 land, and there called the Eel-back Dun, and which afford grounds 

 for doubting the accuracy of the conclusions deduced in a paper, by 

 the late Earl of Morton, ])ub]ished in the Philosophical Transactions 

 for 1820. The title of the paper referred to is " A Communication 

 of a singular fact in Natural History," namely, that a young chestnut 

 mare of seven-eighths Arabian blood, after producing a female hybrid 

 by a male quagga, had subsequently produced, by a fine black Ara- 

 bian horse, a filly and a colt, both of which had the character of the 

 Arabian breed as decidedly as could be expected where fifteen- 

 sixteenths of the blood are Arabian, but in colour, in the hair of 

 their manes, and the markings of the back and legs, bore a striking 

 resemblance to the quagga. 



'J'he author, finding that similar markings are very commonly met 

 with on the Eel-back dun ponies of Scotland, suggests, that as the 

 breed of the mare in question was not pure she may have inherited 

 • the tendency to those peculiar markings. He moreover observes, 

 that the cross-bar markings on the legs are not found in the quagga, 

 but only in the zebra, which is a sjjecies quite distinct from the 

 quagga ; a fact which he considers as completely overturning the 

 reasoning by which the conclusions stated in Lord Morton's paper 



