Part 4 (1/2)
In 1846, a large vine, the black Hambro-grape, {79} ripened its fruit out of doors, and was as fine as any green-house production; but during nine years that the vine has been under my inspection, this was the only time I have witnessed such a result.
We are apt to attribute an abundant or scarce fruit season to temperature alone, but this is an error--for we have before remarked, that though certain lands may be in the same degree of lat.i.tude, the plants which thrive well on one land, will not do so on the other: in fine, that where reason and a.n.a.logy would lead one to expect a particular form of vegetation, a totally different Flora is presented to the view. These facts are indeed suggestive of new and important deductions. Is it yet explained why the town of Birmingham should be free from Cholera? There is a large manufacturing population, a great number of poor, the usual overcrowding of individuals in small chambers, a considerable amount of dest.i.tution and depravity; irregular habits of living, and unwholesome diet, and doubtless many parts of the town, which on investigation would have yielded all the elements usually considered necessary for the localization of the disease: but no--here was some repelling cause, some opposing agent to the generation and propagation of the pestilential seeds. There are no known laws by which inorganic matter could be supposed to observe such a selection, or such an antagonism. Electricity, magnetism, ozone, gases, exhibit no such elective properties that here they will destroy, and {80} there they will spare; that they can almost depopulate small villages, and scarcely find a victim in Birmingham and Bath. But if we suppose a living, and multiplying matter as the cause of disease, many local causes may conspire to arrest the development of the germs, or perhaps, even utterly destroy them.
4th. As to the time of latency, facts crowd upon us indefinitely, as elements of comparison between vegetation generally, and disease in its early stages and history. The seeds of plants are extraordinarily tenacious of life. What a mysterious arrangement of the ultimate particles of matter must there be, by which the vital force remains apparently inactive for many years, and yet when the conditions arise favourable to its manifestation, as it were by an extraordinary fiat, life appears.
Previous to the year 1715, no broom grew in the King's Park, at Stirling; but in that year a camp was formed there, and the surface of the ground consequently was broken in many places. Wherever it was broken, broom sprang up. The plant was subsequently destroyed; but in 1745 a similar growth appeared after the ground had been again broken for a like purpose.
Some time afterwards the park was ploughed up, and the broom became generally spread over it. ”In several places in the neighbourhood of Edinburgh,” says Professor Graham, ”the breaking of the surface produces an abundant crop of Fumaria parviflora, {81} although the same plant had never before been observed in the neighbourhood. It is impossible to say the lapse of time since these were buried, before they were again excited to the performance of all their vital functions.” Dr. Graham also gives another proof of the vital force existing in seeds. ”To the westward of Stirling there is a large peat bog, a great part of which has been flooded away by raising water from the River Teith, and discharging it into the Forth,--the under soil of clay being then cultivated. The clergyman of the parish standing by while the workmen were forming a ditch in this clay, which had been covered with fourteen feet of peat earth, saw some seeds in the clay which was thrown out of the ditch; he took some of them up and sowed them: they germinated and produced a crop of Chrysanthemum septum.
What a period of years must have elapsed while the seeds were getting their covering of clay, and while this clay became buried under fourteen feet of peat earth!”[34]
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What limit can there be to the dispersion of seeds when their vital properties may remain so long unimpaired? The seeds of which we have been speaking were, no doubt many of them, washed away with the waters of the Teith, and carried by the stream into the Forth; and who shall then mark their destination; for we have seen that by such means the most distant lands are supplied with vegetation; for whence come the plants which cover the Coral Islands, unless by the air and the water, and that both contribute, has been incontestably proved. Dr. Lindley states that melon seeds have been known to grow when forty-one years old; maize thirty years, rye forty years, the sensitive plant sixty years, kidney-beans a hundred years. But seeds in general have an indefinite period, apparently, at which they can retain their power of germination; for many of the seeds which had been kept in the herbarium of Tournefort for more than a century, were found to have preserved their fertility.
It has now to be shewn that the germs of disease also retain their vital powers in a state of dormancy during a lengthened period.
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Mead has very judiciously observed, ”to breed a distemper, and to give force to it when bred, are two different things.” He further remarks, that the seeds of the Plague may confine themselves to a house or two during a hard frosty winter, and be preserved, and again put forth their malignant quality as soon as the warmth of the spring gives them force. It is certainly very remarkable that the Plague of London, which commenced at the latter end of the year 1664, should ”lie asleep,” as Mead says, from Christmas to the middle of February, and then break out in the same parish.
It has been also known that an infected bed laid by for seven years had done infinite mischief on being again brought into use. Indeed, it is quite uncertain for how long a period woollen, fur, linen, cotton, and other articles may retain infectious matter in a dormant state. It has been supposed by some that in closely packed bed and body clothes a multiplication of the germs may and does take place, nor do I see any reason why this should not be the case, for these articles contain within their structure the effluvia of the animal body, and they may possibly there find sufficient nutriment for their development. Nees von Esenbeck believed that some of the minute Cryptogamia were re-produced in the air, we are not therefore exceeding philosophical conjecture when we imagine a basis and substratum, though an unusual one, for the germs of vegetation.
Exclusion from air and light, {84} however, as would be the case in packed-up clothes, would _a priori_ give a better colour to the conjecture, as these are the usual conditions necessary for the growth of seeds.
Small Pox and Cow Pox matter, which are now proved to be the same virus, the former modified by having been through a process of growth and maturation in the cow, are both remarkable for exhibiting their active properties after having lain dormant for a considerable time. And each, though so closely allied, retaining its specific properties.
This peculiarity in the history of Small Pox virus suggests a comparison with some phenomena of vegetation, _viz._ that of grafting or budding. The lower Cryptogamia in their fructifications resemble rather multiplication by buds than by seeds. M. Moyen's idea is that every spore or little globule, independently of its neighbouring one, lives, absorbs, a.s.similates, grows, and re-produces on its own account; this is certainly the characteristic of the Torula and the Uredo, and doubtless is so of many other of the Cryptogamia, the Protococcus nivalis is another instance.
Other modes of cultivation produce also great varieties of results of an unexpected kind.
Would any one, says Dr. Walker, imagine that cabbage, cauliflower, savoy, kale, brocoli, and turnip-rooted cabbage, were the same species? yet nothing is more certain than that they are only varieties produced by the cultivation of the Bra.s.sica oleracea, {85} a plant which grows wild on the sea-sh.o.r.es of Europe.
These varieties in vegetables have now become permanent, and though it is supposed that each is liable to return to its original condition, I am not yet certain that such is the tendency. A deterioration is not unlikely to ensue in the course of time, because the propagation by seeds must necessarily very much approach the system of intermarriage, on which Mr.
Walker has so ably written and clearly shewn that as a result we may invariably expect a deterioration of the species. Dr. Darwin has also poetically described what his experience taught him.
”So grafted trees with shadowy summits rise, Spread their fair blossoms and perfume the skies, _Till canker taints the vegetable blood_, Mines round the bark and feeds upon the wood; So years successive from perennial roots, The wire or bulb with lessened vigour shoots, Till curled leaves or barren flowers betray A waning lineage verging to decay; Or till amended by connubial powers, Rise seedling progenies from s.e.xual flowers.”
The minute nature of the germs of disease preclude all possibility of their being submitted, as far as we know at present, to the inspection of the physiologist, but we may infer many facts from results. In the same way, though with humbler {86} ideas, as Cuvier could build up an animal from a single bone, can we by a combination of facts infer the existence of living beings and conjecture their forms. ”The re-production or generation of living organized bodies is the great criterion or characteristic which distinguishes animation from mechanism.” We find the virus of Small Pox, according to Mr. Ceely's experiments, developing itself as a const.i.tutional disease upon the cow, and becoming modified into a form known as the Cow Pox; this resembles the process of cultivation by which a species is converted into a variety, this variety remains for a certain time persistent; the time is not yet known, but it is known that by degrees, as stated above, a deterioration occurs, and fertility becomes impaired, ”a waning lineage verging to decay,” and this has been observed as a feature in the result of vaccination. I believe Dr. Gregory was one of the first to notice this fact, and deemed it necessary to obtain fresh lymph from the cow; this has been done, and it is not improbable, if the a.n.a.logy we have drawn be correct, that the slowly spreading scepticism regarding vaccination may be arrested in its progress. If we can explain the deterioration of cow pox virus on this principle we have a hold at once upon the public, and can a.s.sure them that the efficacy of the proceeding is as certain as in the time of Jenner. The people, I contend, have a right to demand of us the reason why vaccination is not so efficacious as formerly, and I {87} affirm as unhesitatingly that we are bound to give the subject our most earnest attention.[35]
Now concerning the re-production of Cow Pox matter, and a.s.suming it to resemble that of the lower Cryptogamia, we can easily understand how degeneration in a course of years should ensue, for we find that though the Small Pox is a const.i.tutional disease, that produced by vaccine lymph is a local affection, so that it bears the relation that grafting does to vegetation, and it is not improbable that such a modification takes place in the germs by pa.s.sing through or becoming generated in the blood of the cow, that they entirely lose their original and characteristic form of reproduction: the seeds of the disease were originally capable of vegetating, if I may be allowed to use the term, by diffusion through the atmosphere; they now, however, have lost that property, and require to be grafted to exhibit any manifestation of vitality.
How often will the seeds of a cultivated fruit grow? If you bud it upon another plant, you obtain a being exactly like the parent, but this, as we have seen, deteriorates in a course of years, we have also seen that the virus deteriorates; but not to stretch this point to an unseemly length, I cannot avoid expressing my conviction, that these are elements of comparison, possessing an interest and a practical utility of no small value.
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I have before said, that the reproduction in the Cryptogamia, rather resembles budding than seeding. If we observe the Torula, or take the process of all formation, generally it will be found to accord more exactly with the budding than the seeding process, and this peculiarity is not confined to vegetation, it is also a marked feature in the reproduction of infusoria, sponges, polypes, &c.
”New buds surround the microscopic plant.”
The reproduction of plants and animals appears to be of two kinds, solitary and s.e.xual; the former occurs in the formation of the buds of trees, and the bulbs of tulips.