Characteristic Forms of the Sporangia and Spores of Saprolegnia.

I.-A zoosporangium full of nearly ripe zoospores from the skin of a living diseased salmon.

II. An empty zoosporangium, through the centre of which the hypha is growing in order to produce a new zoosporangium. From the fresh growth of Saprolegnia on the diseased jaw membrane of a salmon, cut off and placed in water.

III. A dictyosporangium from salmon Saprolegnia cultivated on a dead fly. The spores have remained in the interior of the zoosporangium, and, after encasing themselves, have there germinated.

IV.-Zoospores of salmon Saprolegnia, germinating in water.

V.-An oosporangium of Saprolegnia from the pike, cultivated on a dead fly. The oosporongia of the salmon fungus in all respects resemble this.

Signification of the letters:-hy, hypha; zspn, zoosporangium; zspr, zoospore; oospn, oosporangium; oospr, oospore; anth, antheridial filament; an, antheridium.

rivers in England and Scotland in Blue Book, C. 2660 for 1880, I would refer all who are desirous of making a more extended acquaintance with the Scientific knowledge of the Saprolegnia Fungus. For the present, I will endeavour, by the aid of the drawings, to epitomise the character of the disease in such a manner as to render it intelligible to those who have never had the advantages of seeing it either with the unaided eye, or under the microscope.

A microscopical examination of a vertical section through a diseased patch reveals, upon its exterior, a number of slender transparent tubular filaments, growing oftentimes in a singularly regular manner, and terminating generally in rounded, although sometimes in tapering, club shaped, or pyriform extremities. These tubular filaments (hypha) are the stems of the plant, which, if traced downwards, are found to have their rootlets ramifying some horizontally in the superficial, middle, and deep layers of the epidermis, others vertically downwards penetrating the true skin, disorganising its structure, destroying its nutritive material, laying open the small blood vessels in its substance, and causing its ulceration and sloughing. These rootlets are the mycelium, and correspond to the "spawn" of our Mushroom beds.

Beyond the margin of the diseased patch, the skin appears normal in structure. The ulceration and disorganization follows the Fungus growth, thus indicating that the Fungus is the primary cause of the disease and not its consequence. The Fungus must therefore be classed amongst the epizoic fungi: its life commencing externally, as is the case with that of the potato disease, vine disease, hop mildew, &c., &c. The Fungus stems are seed vessels (sporangia, zoosporangia, Fig. I., II.) enveloping a colourless granular protoplasm of minute spheroidal cells, (spores, zoospores). The cells rapidly increase in size, and when mature are liberated in an ovoid form as zoospores or living spores from the extremity of the filaments, having attached to them a pair of cilia or tail-like appendages, which give them the power of motion, and which alighting beyond the circumference of the diseased patch are prepared to extend the disease centrifugally. Should the zoospore fail to attach itself to any substance capable of giving it nourishment, it speedily dies. Each sporagium contains swarms of these zoospores.

In some instances, the zoospores germinate within the zoosporangium itself, as is seen in diagram Fig III. (dictyosporangium).

There is yet another method of reproduction. The hyphæ break up into joints which are capable of germination. The short branch of a hypha dilates into a spheroidal capsule with a thick cellular covering within which protoplasm is developed, containing one or more spheroidal masses called oospores. This capsule is called an oosporangium (Fig. V.) Fecundation probably takes place where an antheridium from an adjacent branch of a hypha applies itself to the outer wall of the oosporangium (Fig. V.), and the spores, when liberated from their capsule, are enveloped in a thick tough skin, which enables them to remain quiescent, (as do the spores of the Peronospora infestans-the fungus of the Potato disease-see Woolhope Transactions, 1875, p. 166) and for this reason are called "resting spores."

The well-known fact that the disease is propagated by these zoospores leads

to the consideration as to what circumstances are favourable and what are antagonistic to their growth. The conditions under which the zoospores germinate most readily are the presence of animal and sometimes vegetable matter in a moist state of decay, or even of living animals, especially if the skin has been injured in any way. Warm weather, deficient oxygenation of the water, as from absence of rainfall, form additional causes of its rapid growth; and thus a mild winter and spring encourages it. Pollution of rivers by sewage, refuse from mill factories, infusions of agricultural manures, sheep washing, and other causes to which the disease has been often attributed, is clearly exonerated from the charge of producing it for the very obvious reasons of the disease having been most virulent in rivers particularly free from pollution, such as the river Eden, the river Kent, the river Leven (which flows out of Lake Windermere), and some rivers in California, although of course it is not denied that the greater the amount of decayed animal and vegetable matter present in the water, the more the production of the disease must be encouraged, seeing that it might convert a disease which was simply sporadic into an epidemic. In the epidemic this year in the Wye, the gravel beds were observed by the fishermen to be covered in some places—for instance, at the mouth of the Lugg river—with a layer, several inches thick, of a very filthy deposit.

Any injury that the salmon may meet with certainly renders them very liable to be attacked by Saprolegnia. Mr. Wilmot, engaged in the cultivation of fish in Ontario in 1867 to 1868, found that the fish transferred from one stream to another suffered so much from disease when seized by the head and back, that he introduced the use of indiarubber gloves, and directed that the fish should always be seized by the tail. Although the mortality was diminished by this means, nevertheless, in a year or two many fish died with the fungoid growth appearing first round the tail.

The injuries salmon inflict upon each other, and their low vitality when returning from their spawning beds, render them almost certain to be attacked when the fungus is prevalent.

The causes which tend to prevent the growth of the fungus are numerous. In the first place, cold is as antagonistic to the Saprolegnia as it is to all fungoid growth. Thus Mr. A. D. Berrington, in his last report on the Usk fishery, observes that "the only year in which there was no evidence of disease at all in the Usk river (although carefully looked for) was in the year 1881, following the very severe winter of 1880"; and many other similar instances might be given.

Sea water, or common salt in water when of a sufficiently strong solution, fatal to the growth of the fungus. Mr. Silk (pisciculturist to the Marquis of Exeter,) has in two days cured black bass fish infected with the disease by placing them in salt water. Again, Mr. List (Chief Constable of Berwick,) has, at the instigation of Professor Huxley, kept several diseased salmon in cages at the estuary of the Tweed with the result of so complete a recovery, that upon a microscopic examination no trace of the disease could be discovered by Professor Huxley.

The most antagonistic cause however to the increase of the disease is, beyond

question, the occurrence of a flood on the river, for this not only removes most of the causes tending to produce it, but also carries off the poor weak afflicted kelts into sea water, where many may arrive dead, no doubt, but where others not so badly affected get a chance of recovery. It was a flood of this character that put an end to the disease in the river Wye in the month of May, during the epidemic this year.

As a general conclusion it may be stated, that the disease which kills the salmon is now well proved to be the fungus Saprolegnia ferax. It is this, and this alone, which destroys the fish by its rapid development on the skin. It attacks weak or injured fish by preference, and they have less power of resisting the growth of the fungus, but it is yet capable of attacking salmon which are in the very best condition of health and strength when just fresh from the sea, and of destroying them in a very few days. Professor Huxley suggests the possibility that some rootlets or mycelia of the disease may remain from a former attack, but too deeply seated to have been eradicated by the beneficial effect of the salt water, but as yet there is no proof of this. The cause of the appearance and rapid growth of the fungus has yet to be discovered, but if one thing is more clear than another it is that river pollution does not produce it. The same wonderful mystery attends the development of this microscopic fungus as does that of many others, which, extremely minute as they are, yet by their rapid production produce the greatest changes in organic nature. Their prevalence is possibly due to meteorological causes not yet fully appreciated. The life-history of some of them, however, as that of the funguses which cause fermentation; of the fungus Peronospora which affects the potato; of muscardine (Botrytis bassiana), the fungus which destroys the silkworm; and now, too, we may say the same of Saprolegnia ferax which kills salmon; and of some others also; is beginning to be understood, and as knowledge further advances, the means of checking their production will doubtless be increased. It would be valuable to discover the habitat of the "resting spore,” and some practicable system of exterminating it, and otherwise diminishing the development of a disease which has so many methods of reproduction. Persevere then, oh Woolhopeans! in the study of the minute funguses which has already given so much renown to your Club! Take warning, oh fishermen Injure the fish as little as may be possible! Use your nets sparingly in the early season of the year, when the exhausted fish are on their way back to the sea; and when you do take them, handle them tenderly, as if you loved them. And, lastly, oh conservators and legislators! spare no efforts to purify the rivers. Remove without delay from your rivers all dead, and all badly diseased fish, and bury them deeply, or far better still, completely annihilate every spore by cremating them. Knowing as much as we do about the prolonged dormancy of resting spores, knowing how disturbed the ground may be by the burrowings of rats, moles, earthworms, &c., and that latent spores may thus, at some future period, be again brought to the surface of the ground, and, upon the advent of the next flood or shower, washed into the river, there again to re-exercise their deadly influence; we should recommend providing against this contingency by a system of cremation. Let the bailiffs be supplied with a few faggots wherewith to form