Scientific and General Memoranda. 525 



SCIENTIFIC AND GENERAL MEMORANDA. 



Tyrian Purple Dye. — The shells from which the celebrated 

 purple dye of the ancients was extracted, named by Pliny, the 

 Murex and Buccinum, have given occasion to disputes among 

 modern naturalists as to the species meant. M. Lesson, upon 

 comparing the mollusca now found in the Mediterranean, with 

 Pliny's description, is of opinion the Buccinum is the lanthina. 

 It is a pelagian shell, and extremely numerous. It sustains itself 

 on the surface of the sea by air vesicles, which Pliny calls a glu- 

 tinous wax ; and as soon as it is taken out of the water, there 

 escapes from it a very pure and very brilliant violet rose colour. 

 Each shell contains an ounce of this in the dorsal vessel. By 

 means of alkalies this colour is changed to green. The lanthina 

 abounds equally in the Atlantic as in the Mediterranean ; and 

 at certain seasons the beaches of St. Helena and Ascension are 

 entirely covered v/ith them. From experiments made with this 

 colouring matter, it appears to be a valuable reactive, turning 

 red when treated with acids, and blue with alkalies. Oxalate 

 of ammonia gives a deep blue precipitate, and nitrate of silver a 

 prttey ash blue for painting in water colours. 



Mode in which the common Frog takes its food. — The Rev. Mr. 

 Bree in a communication to the conductor of the Magazine of 

 Natural History, states, — " The friend to whom I am indebted 

 for having first called my attention to this amusing exhibition, 

 was himself introduced to it by mere accident. He happened 

 to be re-potting some green house plants, and meeting with a 

 moderate sized worm among the roots of one them, he carelessly 

 threw it aside into a damp corner near the green house. Almost 

 immediately a frog issued from his lurking place hard by, com- 

 menced his attack upon the worm, and soon dispatched it. An- 

 other worm was thrown to him, which he treated in the same 

 manner. But the amusing part of the business is to watch the 

 manner in which the frog first notices his prey ; and this I can 

 compare to nothing so aptly as to what, indeed, it very much 

 resembles, a pointer dog setting his game : he makes, in short, 

 a dead set at it ; oftentimes, too (if the relative position of the 

 two animals so require it,) with a slight bend or inclination, more 

 or less, of the forepart of the body to one side, just as we often 



