an extraordinary range of form and mode of multiplication is presented by this one species of trypanosome. Space will not permit us to comment on these various phases beyond noting how assuredly such forms would have escaped recognition as belonging to the trypanosome history if seen, before Dr Schaudinn's memoir was printed, by any of our medical commissioners blindly exploring round about the diseases caused by trypanosomes in man and mammals.

One very astonishing and revolutionary fact discovered by Schaudinn we must, however, especially point out. Medical men have long been acquainted with the spirillum,

The full-grown trypanosomes seen in fig. 4 have now been swallowed by the common gnat, Culex pipiens, and are undergoing development in its stomach.

A, shows the spermatozoa, Sp., or microgametes, developing as elongated animalcules from the male cell. The large black mass, z, is the stained nucleus of a blood cell of the owl to which the parasite was adherent. B, shows the now rounded egg-cell, Oo, being fertilised by the liberated spermatozoa, Sp. The fusiform mass on the right is a discarded outer coat of the female trypanosome together with the nucleus, x, of a blood-corpuscle of the owl to which it was adherent. After Schaudinn.

or spiral threads, discovered by Obermeyer in the blood of patients suffering from the relapsing fever of eastern Europe. These were universally and without question regarded as Bacteria (vegetable organisms) and referred to the genus 'Spirochete' of Ehrenberg. They were called

Spirochete Obermeieri; and relapsing fever was held to be a typical case of a bacterial infection of the blood. It is now shown by Schaudinn that the blood-parasite spirochete is a phase of a trypanosome (fig. 7); that it has a large nucleus and a micronucleus or blepharoplast, neither of which are present in the spiral Bacteria; and, further, that it alters its shape, contracting so as to present the form of minute oval or pear-shaped bodies, each provided with a larger and a smaller nucleus. These oval bodies are often engulfed by the colourless corpuscles (phagocytes) of the blood; and it is in the highest degree probable that in this condition they have been observed in some tropical diseases without their relation to the spiral

Further phases of Trypanosoma Ziemanni after fertilisation, which are found in the intestine of the common gnat, Culex pipiens.

a, corresponds to the vermicule phase (ookinete) of the malaria parasite. It is the fertilised egg-cell, now elongated and active in movement. The nucleus is seen, and within the nucleus is the blepharoplast. b and c, elongation and coiling of the ookinete with multiplication of the nucleus corresponding to the formation of the spore-holding cysts of the malaria parasite which are attached to the gut-wall of Anopheles; d, breaking up of the coil into small neutral trypanosomes (neither male nor female). From Schaudinn.

forms being suspected. The corpuscles lately described by Leishman, in cases of a peculiar Indian fever, are very probably of this nature, as are also similar bodies recently described in Delhi sore. On the whole, it may safely be said that the researches of Dr Schaudinn, of which only a preliminary account has yet been published, have widely modified our conceptions as to these blood

parasites, and must lead to important discoveries in regard to diseases caused by them in mammals and in man.

The facts that wild game serve as a tolerant reservoir of trypanosomes for the infection of domesticated animals by the intermediary of the tsetze fly, and that native children in malarial regions act the same part for the malarial parasite and mosquito, suggest very strongly that some tolerant reservoir of the sleeping-sickness trypanosome may exist in the shape of a hitherto unsuspected mammal, bird, or insect. The investigation of that hypothesis and the discovery of the reproductive and

d.

f.

FIG. 7.

Forms of small neutral trypanosomes belonging to the series of T. Ziemanni found in the malpighian tubes of the common gnat. That marked a is also found in the owl's blood, where it is introduced by the bite of the gnat and multiplies by fission, eventually giving rise to the full-sized sexual forms of fig. 4. These small elongated forms are what have been called Spirochæta, and confused up till now with the bacterial parasites known as Spirillum.

a, neutral Spirochaeta-phase showing, n. nucleus and, bl. blepharoplast; b, a smaller individual dividing by longitudinal fission into two; c, a similar individual with the two newly formed fission products extended in line; d and e, further longitudinal fission in progress; ƒ, a smaller Spirocheta-phase; g, resting state or contracted condition of the same; h, resting state of a four-fold individual such as e; i and k, star-like agglomerations (such as are well known in Trypanosoma Lewisii, Brucei, and equinum) due to a coming together of free individuals and not to a fission or budding process. After Schaudinn.

secondary forms of the mammalian trypanosomes are the matters which now most urgently call for the efforts of capable medical officers. But we must not be sanguine of rapid progress, since men of the scientific quality

needful for pursuing these enquiries are not numerous; and those who exist are not endowed with private fortunes, as a rule. At the same time no attempt is made by the British Government to take such men into its pay, or to provide for the training and selection of such officers.

The relations of parasites to the organisms upon or in which they are parasitic, and the relation of man, once entered on the first steps of his career of civilisation, to the world of parasites, form one of the most instructive and fascinating chapters of natural history. It cannot be fully written yet, but already some of the conclusions to which the student is led in examining this subject have far-reaching importance and touch upon great general principles in an unexpected manner.

Before the arrival of man-the would-be controller, the disturber of Nature-the adjustment of living things to their surrounding conditions and to one another has a certain appearance of perfection. Natural selection and the survival of the fittest in the struggle for existence lead to the production of a degree of efficiency and harmonious interaction of the units of the living world which, being based on the inexorable destruction of what is inadequate and inharmonious as soon as it appears, result in a smooth and orderly working of the great machine, and the continuance by heredity of efficiency and a high degree of individual perfection.

Parasites, whether microscopic or of larger size, are not, in such circumstances, the cause of widespread disease or suffering. The weakly members of a species may be destroyed by parasites, as others are destroyed by beasts of prey; but the general community of the species, thus weeded, is benefited by the operation. In the natural world the inhabitants of areas bounded by sea, mountain, and river become adjusted to one another; and a balance is established. The only disturbing factors are exceptional seasons, unusual cold, wet, or drought. Such recurrent factors may from time to time increase the number of the weakly who are unable to cope with the invasions of minute destructive parasites, and so reduce even to extermination the kinds of animals or plants especially susceptible to such influ

ences.

But anything like the epidemic diseases of para

sitic origin with which civilised man is unhappily familiar seems to be due either to his own restless and ignorant activity or, in his absence, to great and probably somewhat sudden geological changes-changes of the connexions, and therefore communications, of great land areas.

It is abundantly evident that animals or plants which have, by long æons of selection and adaptation, become adjusted to the parasites and the climatic conditions and the general company (so to speak) of one continent may be totally unfit to cope with those of another; just as the Martian giants of Mr H. G. Wells, though marvels of offensive and defensive development, were helpless in the presence of mundane putrefactive bacteria, and were rapidly and surely destroyed by them. Accordingly, it is not improbable that such geological changes as the junction of the North and South American continents, of North and South Africa, and of various large islands and neighbouring continents, have, in ages before the advent of man, led to the development of disastrous epidemics. It is not a far-fetched hypothesis that the disappearance of the whole equine race from the American continent just before or coincidently with the advent of man-a region where horses of all kinds had existed in greater variety than in any other part of the world-is due to the sudden introduction, by means of some geological change, of a deadly parasite which spread as an epidemic and extinguished the entire horse population.

Whatever may have happened in past geological epochs, by force of great earth-movements which rapidly brought the adaptations of one continent into contact with the parasites of another, it is quite certain that man, proud man, ever since he has learnt to build a ship, and even before that, when he made up his mind to march aimlessly across continents till he could go no further, has played havoc with himself and all sorts of his fellowbeings by mixing up the products of one area with those of another. Nowhere has man allowed himself-let alone other animals or even plants-to exist in fixed local conditions to which he or they have become adjusted. With ceaseless restlessness he has introduced men and beasts and plants from one land to another. He has constantly migrated, with his herds and his horses, from continent to continent. Parasites, in themselves beneficent