Part 7 (2/2)

It were needless to multiply instances of other endemic and epidemic diseases of vegetables; they are well known by practical observers to be very numerous, and I believe, in most instances, depending upon fungoid growths. The destruction of vegetables by insects, is of a very different nature to that produced by the fungi; it would be as unreasonable to consider the consumption of corn and herbage by locusts, as a disease of vegetation, as the ma.s.sacre and devouring of human beings by cannibals, a disease of the human body.

It is true that insects are exceedingly destructive to plants, but as far as I am able to obtain information, they appear to be so chiefly by their voracious propensities; they consume the structure of the plant in its ent.i.ty, and do not primarily interfere with its vitality. The instance of the vibriones, before-mentioned, seems at first to be an exception {154} to the rule, but this is rather apparent, than real; and it may be made to apply more as a confirmation, than an obstacle to the vegetable theory: for if we may fairly compare the diseases of animals with those of plants, the existence of entozoa in the latter, would be considered an essential point to be substantiated.

Having now considered the question as to the infeasibility of supposing that chemical fermentation is the basis upon which a theory of diseases can be sustained, and having shewn that life is inseparable from infection, and miasmatic generation;--having explained the phenomena of the dispersion of diseases by comparison with the dispersion of plants, and finally, having demonstrated that the physiology and pathology of plants bear so close a relation to each other, and that their epidemic affections depend upon minute organic germs, I submit to the judgment of my readers, whether there is not much reasonableness in the application of the facts to the inference--that living germs are the cause of epidemic disease in man and animals.

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CHAPTER IV.

RESULTS IN PROOF OF THE TENABLENESS OF THE PROPOSITION.

SECTION I.

OBSERVATIONS ON SOME OF THE LAWS OF EPIDEMIC DISEASES.

The results obtained by comparing certain facts connected with Epidemic Affections of animals, with a.n.a.logous affections in plants, afford, from the few instances I shall here notice, a very strong presumption, that a.n.a.logous causes operate in the production of these affections. I have already quoted from Hecker, to shew that previously to, and during the Epidemics of the Middle Ages, the minuter forms of animal and vegetable life appeared to be called into existence, much more abundantly than usual; that famines prevailed in consequence of failure of cereal crops, no doubt depending then, as now, upon the various forms of fungiferous growth. I cannot refrain quoting here, a pa.s.sage or two from our old friend Virgil; for he confirms not only the fact of peculiar showers in {156} connexion with diseases, but he also refers to the rust of corn, thus:

150. ”Mox et frumentis labor additus; ut mala culmos Esset rubigo ...

... Intereunt segetes.”

_Georg. 1._

Then:

311. ”Quid tempestates autumni et sidera dicam?

322. ”Saepe etiam[61] immensum coelo venit agmen aquarum Et foedam glomerant tempestatem imbribus atris Collectae ex alto nubes.”

_Georg. 1._

The occurrence of black showers in this country has been observed during the present year, and I understand that in the fenny countries of the East, the corn has suffered much from the Uredo. I am not mentioning the circ.u.mstances as cause and effect, but merely to call attention to the fact, that unusual phenomena of this kind have been generally a.s.sociated with disease of the animal and vegetable tribes.

The same causes also predispose plants as well as animals, to epidemic attacks of disease. The repeated observations in the public journals on the subject of ventilation, drainage, and over-crowding, render all notice from me needless, to shew that these, though they do not produce the diseases {157} treated of, yet that under the influence of bad air, bad drainage, and over-crowding, epidemics are fostered and spread.

Lastly, says the Count Philippo Re, ”I would remark that if _bad cultivation, and especially bad drainage, does not produce bunt or s.m.u.t, it is certain that those fields, the worst treated in these respects, suffer the most from these diseases_.”

It has been remarked by many observers, that a greater fecundity has attended upon Pestilences, and this has been proved by comparison, that the births in proportion have far exceeded the ordinary limit.[62] In juxtaposition with this observation, I will place the following, not as a proof, but as a remark made quite independently of the subject of which I am treating. ”From the first the diseased ears are larger than the healthy ones, and are sooner matured. What appears singular, but which I have not, perhaps, sufficiently verified, is _that the seeds are more abundant than in a sound ear_.”

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Now these are facts which require amplification, and if these two alone should be shewn upon an extensive field of observation, to apply not only to corn, but to other members of the vegetable kingdom, as I doubt not will be the case, though I am not fully prepared to prove it, it would be difficult to dissociate the fertility of the two living kingdoms from the operations of one and the same, or an a.n.a.logous law.

The epidemic diseases of plants are both infectious and contagious, at times they are observed to be endemic only, and then depending particularly upon some local causes. This is a law of diseases which applies equally to those of men and animals. In connexion with this law is another, which, as far as I am aware, has not hitherto been noticed in connexion with plants.

The potato disease, which excited so much interest and created so much anxiety for the poorer cla.s.ses of society, led the Government of this country to employ the most learned men to investigate the subject, in the hope of propounding some reasons which should explain the cause of the calamity, and thereby deduce a method of eradicating the evil, or, in other words, discover a cure for the disease. Many were the opinions as to the cause of the distemper, which it were useless here to recount, but a method was suggested, to which most people, I believe, looked forward with great antic.i.p.ations, and this was to obtain native seed, and to sow it on virgin soil. Was the end accomplished? No. {159} For though the seed was sown, and the plants grew, the disease still appeared among the newly imported individuals, to as great an extent, as among the native or domesticated plants.

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