the size of sufficiently valuable flat fishes. Thereby the revenue of the plaice fishery of the Kattegat diminishes, because the growth of

Group IV 15 years ago

30

Future limit of size

25

20

15

Number of individuals in one catch

the fishes cannot keep

pace with the rate at which the fishery goes on, in the same manner as the economic revenue of a forest decreases if the wood-cutting is carried on on a larger scale than the growth of the timber permits.

The new convention between Denmark and Sweden regulates the plaice fishery by fixing the limit of marketable fish to 30 centimetres total length. Undersized plaices are not to be brought ashore, but must be thrown alive, if possible, into the water. The plaices taken up by means of the plaiceseine are not injured in any way, as is the case

in the trawling fishery, and can consequently' be set at liberty again. Thus it may happen that a number of fishes will be repeatedly caught by the plaice-seine and liberated, but no undersized fishes are taken away, and the average value of the catch will considerably increase after the introduction of the 30 centimetres limit. Thereby the future maintenance of the stock of plaices in the Kattegat is warranted. As many fishes as can live on this area are allowed to grow there until they acquire the proper size, and there is little probability of their escaping from being caught when they have attained that size on account of the intensive fishery.

This is probably the first case in existence where an international legislation regarding fishery matters is based on scientific research. There can be no doubt that this is the only way for us to find a remedy against the impending ruin of the fisheries of the North Sea area by over-fishing. Blindfold legislation in fishery matters, i.e. legislation which is not based upon thoroughly investigated facts, will be utterly inefficacious.

It is, for instance, a commonly accepted opinion, that the eggs and larvæ of the useful fishes ought to be protected against destruc

tion, and that the fishery should be prohibited at those places, and at that time of the year when the spawning takes place. Such is the leading principle of every rational fish-culture in lakes, ponds, &c. and there is every reason to believe that it will, in many cases, even hold good in sea fishery. In the northern Kattegat, however, it would be utterly useless to lay restrictions of this kind upon the plaice fishery with regard to the eggs and larvæ, since careful scientific investigation has shown that the plaices which habitate the northern Kattegat are not spawned there, but probably outside the Kattegat, in other parts of the North Sea (most probably off the English coast), whence they are drifted eastwards with the surface currents of the North Sea, recently studied by Scandinavian hydrographic observations as well as by the float experiments of the Scottish Fishery Board.

Another remarkable success of the scientific inquiry into the biology of the plaice is the transplanting of young plaices, which is now practised in the interior basins or lochs of the Limfjord. The plaices do not spawn in this fjord, but their growth is considerable.

Experiments have shown that young plaices of 18-22 centimetres, caught and marked in April, reached an average length of 33-35 centimetres in October when transplanted into these inner parts of the Limfjord, probably on account of the abundance of fish food there. In the outer western compartment of the Limfjord, the Nissum Bredning, there is a steady immigration of young plaices (belonging to Groups I. and II.) from the North Sea through the Tyboron Channel, where they, however, cannot grow large on account of the excessive number of individuals compared with the store of food. When these young plaices are caught and transported to the inner parts of the fjord (which can be effected at a cost of 1 or 2 õre for each plaice) they will be worth 25 to 30 ōre seven or eight months afterwards. Of course, all plaices thus transplanted in the spring are caught in the autumn by means of the plaice-seine, and the fishing population of the Limfjord in this manner already earns several thousand crowns yearly, although this transplantation as yet has been practised only on a comparatively small scale on account of certain legal prerogatives which remain to be regulated.

But the living conditions of the various species of useful fishes are manifold, and will be found to be highly different for fishes inhabiting the bottom, like the plaices or other flat fishes, and migratory fishes, such as mackerels, herrings, cods, &c. They will be found different for prey fishes, or those who feed upon the shells and worms &c. of the bottom clay, and for those whose nourishment consists of the freely floating plankton organisms of the upper water layers. For this important group of fishes, to which belong, for instance, the

VOL. XLV-No. 264

X

herrings, the sprat, the sardines, &c., the sea currents, the physical condition of the sea-water with regard to salinity and temperature, and the quality and quantity of the swimming fish food, i.e. the microscopic animals and algæ, which constitute the 'plankton,' so called by Hæckel, are of such vital importance, that we have good grounds to believe that the great migrations of the herrings are wholly dependent upon these circumstances.

The Prince of Monaco suggests that the disappearance of the sardines from the French coast may be due to changes of temperature in the water.

These fishes live on very low organisms of minute size called Peridinia, the habits of which are probably largely influenced by temperature. In investigations on the sardine, made off the Spanish coast by the collaborators of the Prince of Monaco, MM. Pouchet and De Guerne found in the intestine of a single fish a number of Peridinia which might be estimated at twenty millions, without counting those in the stomach and œsophagus. Now this genus Peridinia, although widely spread over all parts of the ocean, where the different sub-species are characteristic for the Gulf Stream, the Arctic area, &c. occur in greatest abundance as constituents of the neritic plankton (Tripos' plankton), or the plankton of the coastal region of the European side of the Atlantic-for instance, the Bay of Biscay, the Channel, and the North Sea in summer and autumn. There is in the later part of the summer a trend of the Gulf Stream towards the Channel and the North Sea region, and the same impact from side of the oceanic surface water, which heaps the food of the sardines, the 'Tripos' plankton, against the coast of France and Spain, a little later in the year sends a warm current of coastal water laden with rich neritic plankton, accompanied by numerous herring shoals as far as into Kattegat. The arrival of the immense shoals of winter herring in November-January in Skagerak is due to another influence, viz. to an invasion by the Polar current from the east side of Greenland upon the Gulf Stream area in the Norwegian Sea in the cold season, which renders great parts of this sea uninhabitable during the winter months and compels the herrings to seek refuge either in the Norwegian fjords or into Skagerak. To such an encroachment of the water from the Arctic side of the Norwegian Sea upon the warm Gulf Stream water of its eastern side seems also to be due the enormous accumulation of the codfishes in January-February towards the spawning grounds inside Lofoten 2 and the Norwegian

2 The vicissitudes of the great cod fishery of Newfoundland are most likely due to similar causes, viz. the conflict of two great oceanic currents of different origin. Another fishery of high economic importance is the herring fishery with drift-nets in the North Sea, east of Shetland and Scotland, which begins in May or June and ends in August. This fishery is also liable to great variations from one year to another. It seems not unlikely that the key to this intricate problem lies in the varying conditions of the sea NE. and E. of the Faeroe islands, where the meeting of the Gulf

coast. Where there is no such external force in action the cods spawn, not crowded into compact shoals, but in widely spread order, as was found to be the case in the North Sea by the German expedition under Hensen and Apstein in February, March, and April 1895. It is strange to think that the physical and biologic state of the most important fishery districts of the world are so imperfectly studied, while fantastic enterprises to reach the North Pole are started yearly. How little do we know at present of the condition of the ocean during the greatest part of the year!

Hitherto nearly all exploring work, biologic as well as oceanographic, has been restricted to the summer months, and we are consequently accustomed to judge the state of the North Atlantic in winter from charts and soundings made in July and August.

Nothing can, however, be more erroneous, since recent Swedish and British researches have shown that great changes take place in spring and in autumn, so that the state of the northern part of the Atlantic is entirely altered in the cold season of the year.

In the winter the already mentioned great invasion of the Arctic stream upon the Gulf Stream area of the Norwegian Sea takes place, and the great western parts of the ocean, which in spring and summer are found teeming with animalic and vegetal plankton, in the cold season become barren and void of life, while an accumulation of marine organisms, both plankton and fishes, takes place towards the European side of the Norwegian Sea and North Sea.

A few years of a systematically organised international survey will serve to clear up the mystery of the migrations of these fishes, and teach us when and where international restrictions upon the fisheries must be accepted in order to counteract the impending ruin of the North Sea fishery by over-fishing.

O. PETTERSSON.

Stream with the eastern branch of the Arctic current takes place. A few years' systematic investigation at the night time (i.e. in the months of March and April) in connection with a similar research of the Norwegian Channel would possibly dispel the apparent mystery of this question.

In the Skagerak the herring in autumn appears with a warm undercurrent of water from the Norwegian Channel, and in February or March vanishes when this relatively warm water of the deeper layers is replaced by the cold and fresh effluvies from the Kattegat and Baltic.

THE PREVENTION OF CONSUMPTION

THE National Association for the Prevention of Consumption and other Forms of Tuberculosis has made a noble and touching appeal to the people of this country to join with the medical profession in an endeavour to prevent and ultimately suppress the most prevalent and fatal of human diseases. This appeal has been most cordially responded to, and the subject evidently at the present moment largely occupies the public mind. Co-operation between the profession and the laity is an essential condition of success. This cooperation must be intelligent, and this intelligence must be educated and wisely directed. It is at all times easier to excite than to control and direct popular movements, especially one in which there is so much which appeals to the emotional as distinguished from the scientific aspects of the question. It is therefore incumbent on those members of the profession concerned in the promotion of this great national work to be precise and explicit in stating their views.

Evidently, certain erroneous impressions have taken possession of the public mind, which should, if possible, be corrected without delay, and one of which indeed has in my experience already led to disastrous results. It is stated with confidence that exposure to fresh air will alone and with certainty cure consumption in every stage and in every form; that this treatment is quite a new departure in medicine-a revelation and a discovery; that it is only in certain sanatoria in Germany, due to private enterprise notably at Falkenstein, that this so-called open-air treatment has been and is carried out successfully; and that the medical men of this country, especially those engaged in the treatment of consumption, have lagged behind their Continental brethren, not only in their knowledge of tuberculosis, but also in its treatment. There is no difficulty in showing that these views are altogether erroneous and misleading. If we examine the treatment at Goerbersdorf in Silesia, the largest and first established of the German sanatoria, we find that the patients are freely exposed to the open air, but that greater importance is attached to the so-called 'forced feeding,' which consists there in trying in every way by example and precept to get the patients to take as large an amount of strong nourishing food as they