THE TECHNOLOGIST. [Dec. 1, 1864. 



220 ON THE REVERSION AND 



present system the cultivator appears to think that climate, food, and 

 the constitution of the insect are all mere secondary considerations to be 

 set at naught, and disregarded with impunity, and then wonders, because 

 he has steadily pursued certain stereotyped rules, at the failure of hi 

 speculation. 



Lest, then, this blind laudation of certain species should lea 

 mischievous results and disappointment among those who are desii 

 entering into the speculation, I shall here beg leave to call the attention 

 of the sericulturist to the well-known fact, that " what is one man's 

 meat is another man's poisou," and remind him that the diet which is 

 admirably adapted to keep up animal heat and to nourish an individual 

 in the vicinity of the North Pole, will be found both unsuitable and 

 highly injurious to health in lower and warmer latitudes. We have but 

 to cast a glance around us in order to perceive that each nation, accord- 

 ing to its climate, differs somewhat from another in the matter of food ; 

 those of the warmer parts of the world being more frugal and less gross 

 in their diet than those of the colder regions. Is it not proverbial, that 

 where a Frenchman, content with thin wines and a few field herbs 

 wherewith to make a salad, would thrive, an Englishman, addicted, as 

 he is, to strong ale, with an unlimited allowance of beef and bacon, 

 would starve outright ? The raw seal blubber, so palatable to the 

 Esquimaux, would be wholly unsuited to the more temperate countries 

 of Europe, and, as a rule, we find that the diet is the simplest in the 

 hottest regions, and becomes gradually more gross as we approach the 

 North, where the cold requires the use of more solid and stimulating 

 food to promote and keep up the animal heat of the body. 



Something of the same kind is assuredly perceptible also among the 

 feral tribes ; the bears, for instance, being far more carnivorous in high 

 latitudes than near the tropics, where fruits, vegetables, and insects con- 

 stitute the animal's food ; but confining my remarks for the present to 

 the larvae of the Bombycidoe or silk-spinners, we find that Nature has 

 ordained that the species in different latitudes shall feed upon different 

 trees. 



It may be said that this arises from the fact that the same trees are 

 not found in these different localities, and consequently that the insects 

 are compelled to seek another food, or to staive ; this, however, does not 

 appear to disclose the true philosophy of the question, and it certainly 

 does not prove that such food in southern regions is equally stimulating 

 with that of northern climes, but rather that instinct teaches the insect 

 to accommodate itself to the provisions provided for it, precisely as a 

 traveller to the northern regions makes use of pemmican, which he 

 discards on returning home. There are, indeed, not wanting proofs that 

 even where the food of one latitude exists in another, the insect will 

 refuse to eat it, as if aware that it is no longer suitable to its wants ! 

 The truth seems to be this, that where a tree and an insect have existed 

 together in, perhaps, a southern latitude, and the tree ceases to grow in 



