« הקודםהמשך »
You who have perhaps known the difficulty of these
before last, I had a black silk worm sent. me from South Carolina, which my friends wrote me word was of a new and much more hardy sort. They grew to an uncommonly fine size, and the cocoons were larger than any I ever had ; but when I came to wind them, I found the texture of the silk so fine, and that it was fixed so firmly together by the gluten that it was utterly impossible to reel off the thread, I hope these are not the sort that Sir William Jones speaks of; for if so, they must be carded before they can be manufactured. I hope my frank will con- , vey a few of them to you, and then you will see the impracticability of extricating the silk f. Whenever you can spare a few moments I shall feel highly gratified in, the pleasure of hearing from you : and I remain, Sir, your much obliged and very sincere friend, Bridgnorth, ?
HENRIETTA RHODES. Sepi. 12. 1792.
OBSERVATIONS SUGGESTED BY THE ABOVE. The public are much obliged to miss Rhodes for the many useful hints she has communicated on this very interesting subject. The foregoing letter seems
* I have not the honour to number this gentleman amorg my relations, though we were schoolfellows, and intimate friends from our earliest is
+ I have many hundreds of these new by me, which I can put to no
fully to prove the practicability of nourishing silk worms entirely upon lettuce, if they be kept in a warm enough temperature of the air, while on that food ; indeed it appears that these worms not only lived upon lettuce, but even preferred it to mulberry leaves.
This fact being established, it next will be necessasy to ascertain which kinds of lettuce answer the purpose best. There are about thirty kinds usually sold in the seed shops, which differ very much from each other. The tenderest appears to me to be that called Spanish montree, and next to that the ice, or cofs lettuce when cabbaged. This last would probably resist rain the best. If any person wishes to make a comparative trial of all the kinds, at the proper season of the year, I shall endeavour to procure the seeds for them, if they have no other opportunity of obtaining them.
As we now see that the silk worm eats lettuce, and thrives upon it in proper circumstances, it is by nó means impossible but other kinds of food may be found which will answer the same purpose. I recommend the chicorium as a proper plant for trial. The chicorium intybus is, like lettuce, a lactescent plant; the common endive is also of the same class.
There is nothing unusual in the circumstance of a certain degree of heat being required to make animals thrive, when kept upon a particular kind of food, that could be dispensed with if they were fed on another sort. Farmers now begin to learn, from experience, that bullocks fed upon turnips, if kept
in a cold place, are apt to be so lax in the belly as not to fatten quickly. If they be kept warm, this inconvenience is not felt; the animal is at all times in a more costive state, and comes on in fattening much more rapidly. This is a branch of rural econoniy not so generally understood as it ought to be ; and miss Rhodes has great merit in having suggested the idea that the health of the silk worms may be affected by the same circumstances,
As to the article light; it is very possible I may be mistaken in that respect, having formed my opinion merely from the report of others. When I said that windows might be saved in houses to be made for silk worms, it was my intention huwever only to suggest that such large windows as are required in stoves for plants, are by no means necessary; so that the great expence of glass might be saved. Whether this lady's opinion, that light is of great utility to the silk worms, or the opinion of Mr Wright of Paisley, with several others, that they thrive better in the dark, be the best founded, I pretend not to say ; but, as there is a doubt on this subject, it would seem that if the worm be aifected at all by this circumstance, it can be but in a slight degree, so that it cannot be a matter of very great importance. It is proper however it should be adverted to by experimenters.
However this may be, there seems to be no reason to hesitate in agreeing with miss R. in approving a south exposure, where that can be commanded ; not only because that is the warmest, and therefore will save most fuel ; but also because the heat thus produced is less liable to generate noxious vapours, than that by a stove. I should think therefore that a south exposure, with a few glazed windows, and a conside, Table number of windows closed with fhutters, that could be opened during the day time, when the sun shone bright, and the weather was in other respects favourable, would be the most eligible.
Every person who has had the management of silk worms on a large scale, complains of the noxious vapour that is generated by them, unless they be kept very clean, and the house properly ventilated. Dr Anderson in Madras has found this kind of ventilation so necessary for the health of the animal, especially in damp weather, that he has contrived a kind of cane matting for admitting the air freely ; which has there answered to admiration. It is surprising however that in Italy, and other warm climates in Europe, where the silk worm has been so long reared, so few contrivances should have been adopted for obviating this inconvenience; for it seems to be an undeniable fact, that the silk worm itself dies in great numbers, in every case where this article of cleanliness is neglected.
By some late experiments made by M. Faujas de St Fond, and recorded in his history of Languedoc, it appears that the silk worm is much hurt by this foul air. From the experiments of Mr Ingenhouz we also know that all decaying leaves produce mephitic air in great abundance ; and as silk worms are constantly fed upon leaves in this state, it must necessarily abound very much in the places where they are kept, if proper means are not taken to remove it. As this mephitic vapour is more weighty than com
mon air ; and as the silk worm is in Italy always kept upon solid tables or shelves, which will prevent it from sinking below them, it follows, that the worms themselves, unless when the house is freely ventila. ted, must be always kept in the mephitic region ; and if they are not suffocated by it directly, like the dogs which are thus poisoned in the grotto del Cane in Italy, they may be subjected to various disorders that prove
hurtful. This seems to be indeed one of the unobserved causes of those unaccountable mortalities that sometimes destroy the best founded hopes of the silk rearer.
If this should be the case we shall probably be able to obviate it by adopting a cleanlier mode of management than is there practised. Dr Anderson of Madras has thrown out some hints that will greatly fa. cilitate this business.
One of the most difficult branches of the management of the silk worm hitherto is the cleaning without bruising them. To avoid this inconvenience, the peasants in France and Italy frequently allow the whole litter to remain without ever cleaning them, which is the cause of that unwholesome stench, that has been so often remarked by those who visit the places for rearing silk worms in these countries. This difficulty, he finds, may be effectually removed by providing a net; or what would be still better, a wire bottomed frame, wrought into large meshes like a riddle. Have that made of a size exactly sufficient to cover the wooden box in which the worms are kept. When you mean to shift them, spread fresh leaves into the wire basket ; and let it down gently over the worms