Retrospective Criticism. 557 



experience gave me confidence, and I have hitherto been well 

 satisfied with the result : the specimens have remained per- 

 fectly supple, and the colours not more injured than by simply 

 diluted spirits. My experience not being yet sufficient to 

 enable me to decide on the most eligible dose, I should re- 

 commend those who may feel inclined to try this plan to make 

 their own observations ; to pay attention to the quality of their 

 sublimate ; and at the same time not to take fright too hastily, 

 as I was very. near doing myself last summer, when, having put 

 several specimens of Mylabris variabilis Latr. into a bottle, 

 I found, a few minutes afterwards, the colours of their trans- 

 verse bands nearly discharged. I caught some others which 

 were killed by steam, without the slightest injury; and, consi- 

 dering the first as spoiled, I left them in the spirits, in order 

 to try the effect of a longer steeping : at the end of a fortnight 

 they were set, and miserable enough they looked ; after two 

 or three days the colour began to deepen ; in three weeks' 

 time they were not to be distinguished from the others ; and 

 at the present moment any slight difference that can be dis- 

 covered is in favour of the poisoned ones. After all, I believe 

 that the greatest security is obtained by frequent inspection, 

 and the immediate application of a drop of solution. of sub- 

 limate, to any individual who may show symptoms of having 

 been attacked. — P. J. Brown. Thun, Canton of Berne, Swit- 

 zerland, April 5. 1833. 



Mr. Nicholson's Account of the Bed Snow seen by him in 

 Prince Regent's Bay. (Vol. II. p. 321.) — I have no doubt of 

 his having given a faithful description of what he saw ; but 

 cannot for a moment suppose it to have been the genuine 

 Protococcus nivalis. Assuming the latter to be the substance 

 which imparts the red colour to snow, I shall not give an 

 opinion as to its identity with what Captains Ross and Parry 

 and Raron Wrangel found on limestone, &c, of which I know 

 little but what is related in Dr. Greville's Scottish Cryptogamic 

 Flora ; but must protest against the auk's dung observed by 

 Mr. Nicholson bearing any resemblance to the colouring 

 matter found occasionally on the snow of the higher regions 

 of the Pennine Alps. As my personal acquaintance with this 

 latter is, however, very limited, it may be proper to detail my 

 experience, in order to prevent my few observations from re- 

 ceiving greater credit than they are entitled to. The first 

 time I was gratified with a sight of it was six or seven years 

 since, during an excursion from the St. Bernard. When at 

 a long distance from the convent, and at a considerably greater 

 elevation, on crossing an extensive plain of snow, my attention 

 was arrested by a spot strongly tinged with red, towards 



