interruption to systematic study, together with all the routine business which constitutes so severe a tax upon the time of a man filling an important official position, do not appear to have damped his energies, nor subdued his fondness for research. His multifarious writings on so many chemical, physiological, and pathological subjects, his works on Ceylon and the West Indies, his life of his brother Sir Humphry, and his edition of the latter's works, are so many standing memorials of what may be accomplished, even amidst the numerous distractions of an army medical life, and are so many bright examples to be followed. Nor do the enervating influences, which so frequently operate on a man, much of whose life has been spent in hot climates, appear to have repressed his mental activity, for, at the last meeting of the British Association, he contributed several papers to the Chemical, Zoological, and Physiological Sections. And that his mind is keenly alive to the importance of many of the subjects of physiological discussion of the present day the work before us is a sufficient proof.

Of the various memoirs contained in this volume, some of the most interesting are those which detail observations made upon fishes, more especially on the Salmonida. There is no subject, Indeed, connected with fish and fishing, which has, for some years back, excited more interest and general attention than the propagation, habits, and distribution of that king of the Salmonide, the Salmo salar. When the cry went forth that our rivers were becoming drained of fish, that many indeed were already exhausted, and that an important article of food was rapidly disappearing, statesmen, economists, and naturalists actively bestirred themselves to endeavour to ascertain the cause of this failure. Select Committees sat for weeks taking evidence, Special Commissioners perambulated the country, men of science performed experiments, bills were introduced into Parliament, and after much fighting between the representatives of opposing interests, Acts were at length framed for the better regulation and protection of our salmon fisheries. Much of the loss and waste of this valuable fish has undoubtedly arisen from the wanton destruction of the ova in the spawning beds, and great efforts are now being made, more particularly in Ireland and at Stormontfield on the Tay, to remedy this by artificial hatching and rearing. It is of considerable importance, therefore, that we should possess some definite information as to the conditions which are favourable or unfa

Dr. Davy

vourable to the preservation of the life of the ova. supplies us with some very interesting observations on the ova of the salmon, and charr, with especial reference to the action on them of different agents, and to their power of resisting exposure and various degrees of temperature. Some of these observations were undertaken at the request of Mr. Darwin, in order to aid in an inquiry into the geographical distribution of fishes. Mr. Darwin wished to have tested, by experiments on the impregnated ova, what they were capable of bearing without the loss of vitality, and under exposure to circumstances such as might be compatible with their being conveyed from one river or lake to another, adhering, for instance, to the plumage, beaks, or legs of birds. With the view of assisting in the determination of these questions, Dr. Davy tried the effects on the ova of exposure to the atmosphere; exposure to moist air; exposure in air and water to a temperature at or below freezing point; exposure in water to a temperature of or above 70°, and the action on the ova of salt and brackish water. From these experiments he concludes

"1st. That the ova of the salmon in an advanced stage can be exposed to the open air, if dry, but a short time, at ordinary temperatures, without loss of vitality; but for a considerable time, if the temperature be low and if the air be moist: the limit in the former case not having exceeded an hour, whilst in the latter it has exceeded many hours.

"2nd. That the vitality of the ova was as well preserved in air saturated with moisture, as it would have been had they been in water.

"3rd. That the ova might be included in ice without losing their vitality; but that if exposed to a temperature many degrees below the freezing point, probably effecting their congelation, they were deprived of their vitality.

"4th. Both the ova and young fish were capable of bearing a temperature of about 80° or 82° in water for a moderate time with impunity, but not without loss of life at a higher temperature, any exceeding 84° or 85°.

"5th. That a degree of saltness of water, equal or nearly equal to that of sea water, is pretty speedily fatal both to the ovum of the salmon and to the young fish; that the same effect is produced on the young fish by brackish water of sp. gr. 1.016, but in a longer time; and that when the solution is so diluted as to be reduced to the sp. gr. 1.007 the advanced ovum may be hatched in it and the life of the young fish may be sustained in it for many days, but with diminishing power."

Finally, the experiments show that it is quite possible for the ova to retain their vitality a sufficient period, under such conditions as they would be placed in supposing them to become temporarily attached to the hairs of mammals or feathers of birds, to permit of their transit, even to a considerable distance, from one lake or river to another. And it is by such agencies undoubtedly that the tarns or small lochs lying far up the sides of many mountains have originally become stocked with fish, and species widely distributed. The

last series of experiments, those, namely, which prove the destructive influence of salt or brackish water on the ova or young fry, are also of much interest. For they seem to us to furnish a satisfactory explanation of the strong instinctive impulse which forces the salmon, as its spawning time approaches, to ascend long and rapid rivers, and to strive to overcome the numerous obstacles, both natural and artificial, which obstruct its path, and so to place the ova and young fry far enough from this source of danger. Another series of experiments performed on the charr have proved, as one would from à priori reasoning have been led to expect, that the power of resisting an undue increase of temperature is possessed in a higher degree by the ova in an advanced, than in an early stage of development, and that the power of bearing distant transport and of retaining life in moist air is in like degree increased with age.

Dr. Davy also communicates some observations on a subject which attracted some attention about ten years ago, bearing on the impregnation of the Salmonida. Statements were made that the ova were impregnated before exclusion and that in the artificial mode of breeding it was not necessary to apply the milt to the roe. These statements were not in accordance with the experiments instituted by Mr. Shaw, Mr. Young, and Mr. Ashworth. And from various trials which Dr. Davy has made by placing ova, obtained from a fish living in a stream in which male fish were known to be present, in circumstances favourable to their development, except that no milt was added to them, nothing but negative results have been afforded. And, indeed, an examination of the organs of generation, both of the male and female fish, is in itself sufficient to show that an act of copulation is hardly within the limits of probability.

There is much interesting information in this volume on the generation and early stage of life of the charr (Salmo willughbii), a fish which in its distribution is exclusively confined to the English Lake district, and even there is limited to a few of the many lakes of that district. But there are other subjects which are equally if not more deserving our attention, and to the consideration of some of these we shall now proceed.

That the blood coagulates when drawn from the body on exposure to air, and that under certain conditions coagulation takes place within the body, are facts which have attracted the attention of physiologists from the earliest times. But though these facts have been generally recognized, yet there have always been many difficulties in

the way of giving a satisfactory explanation of the cause of this coagulation, and many ingenious hypotheses have been framed to account for it. About ten years ago it was announced that the Astley Cooper Prize for 1856 would be awarded to the best essay on this subject, and Dr. B. W. Richardson was the fortunate competitor on whom this valuable prize was bestowed. The theory advocated by this physiologist attributed coagulation to the escape from the blood of a small quantity of the volatile alkali ammonia, and led to the conclusion that the phenomenon was purely chemical in its nature. This theory was supported by a large number of elaborate and very ingenious experiments, and for a time met with much acceptation. In spite, however, of the brilliancy, simplicity, and apparently conclusive nature of many of these experiments, there were always a few cautious inquirers who hesitated to give in their adhesion to the ammonia theory. Amongst this number was Dr. John Davy, with whom the physiology and pathology of the blood had long been favourite subjects of investigation. His thesis submitted to the medical faculty of the University of Edinburgh on the occasion of his graduation in medicine, so far back as the year 1814, was entitled, "Tentamen experimentale quædam de sanguine complectens." And a section of this thesis was devoted to the subject of the blood's coagulation.

In the volume before us, Dr. Davy has reprinted a Memoir on the Coagulation of the Blood contributed to the Transactions of the Royal Society of Edinburgh, in the year 1859, the year after the publication of Dr. Richardson's Essay, and since that time he has communicated additional observations on the same subject to the meetings of the British Association in 1862 and 1863. From the observations and experiments, mostly made on the blood of the common fowl, he concludes that the coagulation of the blood is not dependent on the escape of ammonia, and further that the presence of ammonia in the blood is not the cause of its fluidity. At one time, indeed, he doubted, whether ammonia was even a normal constituent of the blood, but from his latest experiments, related at the last meeting. of the British Association, he is disposed to agree with Dr. Richardson in enumerating the volatile alkali as present in a small proportion in that important fluid.

But Dr. Davy is not the only physiologist in this country who has disputed the accuracy and completeness of Dr. Richardson's theory. In a paper published in the Edinburgh Medical Journal

for April 1858, Professor Lister of Glasgow, then Assistant Surgeon to the Royal Infirmary of Edinburgh, whilst expressing his agreement with Dr. Richardson in ascribing the coagulation of blood drawn from the body, to the escape of a small quantity of free ammonia normally holding the fibrine in solution, yet questions the applicability of the theory, to explain the coagulation of blood within the body, such as occurs in aneurisms, and in inflammation of veins and arteries. So that whatever amount of truth the ammonia theory may contain, yet by leaving certain phenomena unexplained, it does not embrace the whole truth. Since the publication of that paper, Professor Lister has applied himself anew to the investigation of the subject, and has embodied many of his experiments, with the conclusions he has drawn from them in the Croonian Lecture delivered before the Royal Society, 11th June, 1863. In this lecture he has renounced even the qualified belief which he formerly expressed in the ammonia theory, and now comes to the conclusion, which Dr. Davy had already arrived at, that the coagulation of the blood is in no degree connected with the evolution of ammonia. Not satisfied, however, with simply pulling down the scientific edifice which Dr. Richardson had constructed from and based on his numerous ingenious experiments, as Dr. Davy had contented himself with doing, Mr. Lister has aimed at erecting a new one in its place. The following extract from his Croonian Lecture, may be looked upon as embracing the chief points of his theory :

"The real cause of the coagulation of the blood, when shed from the body, is the influence exerted upon it by ordinary matter, the contact of which for a very brief period effects a change in the blood, inducing a mutual reaction between its solid and fluid constituents, in which the corpuscles impart to the liquor sanguinis a disposition to coagulate. This reaction is probably simply chemical in its nature: yet its product, the fibrine, when mixed with blood corpuscles in the form of an undisturbed coagulum, resembles healthy living tissues in being incapable of that catalytic action upon the blood, which is effected by all ordinary solids, and also by the tissues themselves when deprived of their vital properties."

In a short paper on the acrid fluid of the Toad, Dr. Davy returns to a subject which had attracted his attention so far back as the year 1826. From his inquiries, as published in the Philosophical Transactions of that year, he concluded that the fluid secretion of the cutaneous glandular structure of the toad is simply acrid, an irritant, offensive as such, but not a poison,-as had been for so long a period, and indeed still is the popular belief. These conclusions of Dr. Davy were, it would appear, opposed by M. M. Gratiolet and S. Cloez, two French physiologists, who from their examination of the