'278 I'HILOSOrHlCAL TRANSACTIONS. [aNNO 1778. 



nicfire deep in the bowels of the earth, and, mixing with water at the time of 

 its explosion, formed a sort of natural mortar or cement. The Dutch reduce it 

 again to its pristine state of puzzolane. 



//. Of the Heat, &c. of Animals and Vegetables* Ihj Mr. J. Hunter, F.R.S. p. 7. 



As I had formerly, (says Mr. II.) in making experiments on animals, relative 

 to heat and cold, made similar ones on vegetables, and had generally found a 

 great similarity between them in these respects, I was led to pursue the subject 

 on the same plan ; but I was still further induced to continue my experiments on 

 vegetables, as there seemed to be a material difference between them in their 

 power of supporting cold. From observations and the foregoing experiments it 

 plainly appears, that the living principle will not allow the heat of such animals 

 to sink much lower than the freezing point, though the surrounding atmosphere 

 be much colder, and that in such a state they cannot support life long; but it 

 may be observed, that most vegetables of every country can sustain the cold of 

 their climate. In very cold regions, as in the more northern parts of America, 

 where the thermometer is often 50° below 0, where people's leet are known to 

 freeze and their noses to drop off if great care be not taken, yet the spruce-fir, 

 birch, juniper, &c. are not affected. 



Yet that vegetables can be affected by cold, daily experience evinces ; for the 

 vegetables of every country are affected if the season be more than ordinarily 

 cold for that country, and some more than otiiers ; for in the cold climates 

 abovementioned, the life of the vegetable is often obliged to give way to the 

 cold of the country : a tree shall die by the cold, then freeze and split into a 

 great number of pieces, and in so doing produce considerable noise, giving loud 

 cracks which are often heard at a great distance. In this country the same 

 thing sometimes happens to exotics from warmer climates : a remarkable instance 

 of this kind happened this winter in his Majesty's garden at Kevv. The Erica 

 arbores or tree-heath, a native of Spain and Portugal, which had kept its health 

 extremely well against a garden wall for 4 or 5 years, though covered with a 

 mat, was killed by the cold, and then being frozen split into innumerable pieccs.-J- 

 But the question is, is every tree dead that is frozen .'' I can only say, that in 

 all the experiments I ever made on trees and shrubs, whether in the growing or 



* Of this ingenious paper the latter part only, which relates to the heat of vegetables, is retained in 

 these Abridgments; the former part, which contains the experiments on animals, being reprinted in 

 Mr. H.'s Observations on lire Animal CEconomy. 



l' This must be owing to the sap in the tree freezing, and occupying a larger space when frozen 

 than in a fluid state, similar to water ; and that there is a sufficient quantity of sap in a tree newly 

 killed is proved by the vast quantity which flows out upon wounding a tree. But what appeared 

 most remarkable was, lliat in a walnut-tree, on which I made many of my cxpeiimenls, I observed 

 that more sap issued om in the winter tlian in tlie summer. In the summerj a hole being bored, 

 scarcely any came out ; but in the w inter it flowed out abundantly. — Orig. 



