Let us now inquire into the power which fungi have of generating disease. Their influence upon plants has never been doubted: first, because their ravages are too well known, too serious, to admit of dispute; and, secondly, because their malific agency upon structures of a low organisation, allows of more easy demonstration, than when highly organized and sensitive tissues are the seat of their operations, and when more various forces and conditions are to be considered.

It is no difficult matter to show that dry-rot, as it is termed, would be a comparatively slow process, were it not that the fungus is present, to insinuate itself among the fibres of the wood, to give admission to air, and to yield oxygen, which hastens the already commenced decomposition; while at the same time the living cells abstract chemical elements from the woody fibre, and fan into activity the eremacausis or slow combustion of the decaying tissue. Equally obvious is the fact, that without yeast, wort would undergo but little fermentation, and that if all vegetable organisms were excluded, no proper fermentation would result; for even in the case of wine, which is conducted without the artificial aid of yeast, I have found that it is really the source of the fermentation.

We may assume, then, as a fact, which few will deny, that a living vegetable para-site upon other vegetable cells, must excite in them a chemical action, equivalent to fermentation, for it can not grow without so doing; and that even supposing the cells themselves were able to resist this action, the juices of the plant, not possessed of the same vital resistance, must succumb to its influence. Whether this alone be the real secret of its power, affects not the question. If the juices are decomposed the cells must suffer, and the morbific agency is at once apparent. But there is another point in which their action is not unimportant, viz, the power which fungi have of inserting themselves among the cells and tissues. Physiologists, and especially medical writers, overlook this fact, that a ceil confined in a limited space, and at the same time undergoing development, must expand in some direction, and the force thus generated is almost incredible. Many of you have no doubt seen a strong wall pushed down by the growth of a tree; that this, by the expansion of soft and otherwise yielding cells.

But perhaps a more impressive fact is, that simple cellular fungi, growing under large stones, have raised them from their beds to the height of some inches, even when the stones were several hundred pounds in weight; and yet so soft is the structure of the plant that it might be crushed between the finger and thumb. Here is a power not to be ignored when discussing the influence of parasites. Let us see how it applies to the production of disease in animal tissues. Each individual cell, it must be borne in mind, possesses the same motor power; it is only their combined action which yields great results such as the above. Suppose, then, a single tube inserted into the skin and impinging upon a nerve filament, would you not expect that nerve to resent the intrusion? Would it not do so if any other foreign body of the same size were introduced? How much more then, if, in addition to mere mechanical irritation, the cell proceeds to abstract or decompose the fluids. That it does this, which is indeed the essential function as a scavenger, we see in favus and ring-worm, where, especially in the former, the odor produced by it is intolerably fetid and irritating.

It is clear that what with the actual pressure of the outspreading fungus, and the irritating products which it engenders, there are strong prima facie grounds for believing that the fungus does actually produce disease.

Then, again, if proof were wanting, observe the peculiar character of lichen annvlatus, fairy-rings in miniature, presenting all the characters that fairy-rings do, and showing clearly enough that the fungus and rings of inflammation proceed pari passu.

The form of the disease will be determined by several minor conditions affect-ing the growth of the parasite; these we have before mentioned as warmth and moisture, suitability of food and density of tissue, all of which influence the development of the plant; thus we find in Lichen, one form; in Pityriasis, another; in Favus, a third, and so on; the spread of the disease being co-equal with that of the plant, and the degree of passive resistance which the tissues offer to its inroads.

It must be admitted here, as in the case of plants, that an unhealthy condition of the structures and fluids is necessary to the development of a parasite, for without these it would be incapable of establishing itself. The first attack would in a healthy body be at once resented, and the intruder repelled.

I would remark before concluding, that those diseases which are probably-considered as of a parasitic origin, have recently been shown by clinical observation to be identical, and capable of merging one into another by imperceptible gradations; thus establishing the fact which I had asserted from experimental inquiry and the development of the parasites.

In conclusion, a word or two as to the treatment of this class of diseases may not be out of place.

The primary consideration will at once suggest itself, that since the fungi can only attack an enfeebled system, it is essential for the cure of the disease that the general health be restored by treatment appropriate for that purpose; for we can not expect a successful result while this important cause is still in operation.

The remedies which have attained celebrity as specifics, have little claim to be considered, since, if we except arsenic, which, by-the-way, is only useful when it is pushed to a dangerous extreme, they are all of but little value.

Of the topical applications I may observe, that my own experience of them is, that they are either inefficient or dirty, or both. The one to which I trust almost solely, has this to recommend it, that it is neither.

Its action is founded on what ought to be our guiding principle in the treatment of these cases, viz., the destruction of the parasite; and this, from extended observation, I believe to be effected by the Tincture of Iodine, far better than by any mineral or other agent we can employ; at the same time its application is unattended by any inconvenience.

It is simply an alcoholic solution of Iodine, thus: Take of Iodine, 1 drachm; Iodide of Potassium, half a drachm; Alcohol, one ounce; solve. Paint the diseased part every day or on alternate days; omitting it for a day or two if the skin becomes sbre, then resume it, and continue the application until the disease has disappeared.

As yet I have met with no case which has resisted steady treatment of this kind, neither do I believe that I am likely to do so.

[The above is a subject little understood, but of profound interest, and is ably treated, though we can not say that we agree with all the author's conclusions. The paper was read before the Botanical Society Of Canada, from whose proceedings we copy it - ED].