with which we have been working during the past year and which presents several extremely interesting facts. The organism in question was encountered by accident in the laboratory. Several stains of relapsingfever spirochetes are maintained in the laboratory by the inoculation of blood from rat to rat. For some reason the rats begin to die, usually within forty-eight hours.

An investigation developed the fact that there were no bacteria present recognizable either by the microscopic or cultural method. On the other hand filtration tests and inoculation of the filtrates showed that we were dealing with something very small, how small we do not know, but it is safe to say that it is probably the smallest thing that has yet been. recorded. The facts which form the basis for making this statement are twofold. First, it passes readily through the finest filters, such as the Pasteur B and the Doulton. We have not found one that it will not go through. Even the collodium sac and the agar filter, if not too thick, are permeable to this virus. The fact that it will go through a thin layer of collodium and agar is very suggestive of the smallness of the organism. Second, it is apparently not centrifugable. On centrifugation at high speed we should be able to throw the organism provided it is heavier than the liquid in which it is. The common bacteria, as is well known, are very easily centrifugated from the liquid. Of all the ultramicroscopic organisms, I know of none that resists centrifugation unless it be one which we are studying. Submitted to a series of tests at a speed of eight thousand revolutions per minute, for varying periods of time up to twelve hours, the liquid at the end of such tests was just as active on the top as on the bottom. In other words nothing was thrown down by the severest centrifugation. This simply indicated that the organism is extaordinarily minute.

Another interesting feature is the fact that the blood, in extremely small doses, is infective. This particular virus is always fatal to rats, and it is fatal even if we inject extremely minute quantities of the blood, -quantities that are comparable to a fraction of a corpuscle. Usually one billionth of a cubic centimeter will infect and we have obtained infections with one ten-billionth and even one one-hundred billionth of a cubic centimeter. We can well imagine that in these high dilutions only a few organisms, possibly but one, are present.

The ultramicroscopic organisms, it is clear, are characterized, first, by being filterable, and second by being invisible. The latter property. of course, is conditioned by our present limitations and new methods may enable us to demonstrate many of the members of this group. As a matter of convenience it may be well to designate these organisms as "ultrasomes." which term simply summarizes the above characteristics and is without prejudice as to whether they belong to the bacteria or protozoa.

The known ultrasomatic diseases are about equally divided between man and the lower animals. Yellow fever, dengue, pappataci fever, poliomyelitis, rabies, and aphthous fever, foot and mouth disease of cattle, and incidentally of man, have been most studied as regards their filter

able virus. Exanthemic typhus, smallpox, vaccinia, mumps, scarlet fever, et cetera, are probably due to similar organisms.

Of the animal diseases we could perhaps mention half a dozen. In the case of cattle we have foot and mouth diseases, rinderpest, pleuropneumonia and vaccinia or cowpox. Two such diseases are known in horses; one is prevalent in this country, particularly in the west and south, and is known as pernicious anemia or swamp fever. The South Africa horse sickness is due to an organism of this kind. The blue tongue of sheep, sheeppox, rabies, canine pest, chickenpest, bird molluscum, and hog cholera are further examples of thoroughly studied diseases due to filterable organisms or ultrasomes.

I will not go into the discussion of these different diseases, but will limit myself to one example, that of poliomyelitis. Up to the summer of 1909 we knew absolutely nothing as regards the cause of this disease although for some years it has been supposed to be infectious. Several workers isolated various kinds of bacteria but the work was not convincing. In the summer of 1909, Lansteiner and Popper demonstrated that if monkeys were injected with brain or cord suspensions from a case of poliomyelitis, they contracted the typical disease and died of it. They tried to reproduce the experimental disease but failed to do so, and the reason was partly due to the fact that they employed the intraperitoneal method for injecting their material. A short time afterwards, in the fall, Doctors Flexner and Lewis began their studies which have contributed greatly toward clearing up the etiology of this disease. Previous to this they had attempted but had never been able to infect animals. They were now naturally in a position to profit from the results of the Viennese workers and so they inoculated monkeys with poliomyelitis material, placing it into the cranial cavity, subdurally. They succeeded not only in producing the disease, but also in doing what others had failed to do, namely, reproducing the disease from monkey to monkey. The virus is present in the spinal cord and brain matter and if the inoculation is made directly into the brain the disease is most always transmitted. In this way the virus has been kept by Flexner for two years and has gone through twentyfive or more successive passages from animal to animal.

After this fundamental work, it became possible to approach the question as to what was the cause, and since microscopic examination had failed to reveal anything, the natural thing to do was to try the effect of filtration. Infection followed the injection of such filtrates, hence in the fall of 1909, proof was furnished that this disease was due to an untramicroscopic organism. All efforts to demonstrate its presence by microscopic means have thus far been unsuccessful. The only way by which the presence of the virus can be demonstrated is by its effect on the animal.

A large number of very interesting facts have been acquired by the workers in this country, in France, England, and in Germany, and it will be possible for me to touch only upon a few points. First, I may say that the virus, while especially present in the central nervous system is in the blood, early in the infection; also, in the organs, glands, et cetera,

so that it is possible at times to demonstrate its presence by inoculation of such material. Furthermore, this virus, like that of rabies and chickenpest and the rat virus referred to, is quite resistant. Mixed with fifty per cent glycerin it retains its virulence for months-a striking analogy to the virus of vaccinia, rabies, rat, et cetera. Also, if the virus is kept in the ice-box at low temperature it will retain its virulence for a considerable length of time. Unlike the rabic virus, it cannot be attenuated by desiccating the cord over sulphuric acid or potash. It was hoped that the Pasteur method might be utilized as a preventive measure but the method is not applicable since the virus is not attenuated, but destroyed.

Its virulence is increased by successive passage through the monkeys, so that it will always kill, whereas in the beginning it will not do so in most cases. In the animals which recover there is something present in the blood that will destroy the organism, and that destruction is manifested best in the test-tube. For example, if the serum from a recovered animal or child is mixed in the test-tube with a fatal does of the virus and then is allowed to stand in the incubator, or room temperature, or in the ice-box, the mixture when injected afterwards into a monkey will not produce the disease. In other words, a germicidal substance is present in the serum of the recovered animal. This naturally suggests the possibility of using such serum to prevent, and perhaps to cure the disease. Some tests in this direction indicate that it may be possible to realze that hope. It is difficult, however, to increase the immunity of the animal to any great extent; successive inoculations do not increase the germicidal constituent and consequently the serum is never active. If, however, a sufficiently large amount of the active serum is introduced by the subarachnoid method, instead of into the peritoneal cavity, and the animal is then inoculated with a minimum infective dose of the virus, no infection will result. This is the extent to whch investigations of this kind have proceeded with poliomyelitis. It is possible that a suitable animal will be found which can be hyperimmunized sufficiently so as to yield a serum which can be used in practice.

Yellow fever is an old story, due to a filterable, ultravisible microorganism. I simply refer to it at this point in order to call attention to the fact that yellow fever, as well as several other diseases of this type, are spread through bites of insects. We have thus some ultramicroscopic organisms which, like poliomyelitis, are spread by contact, from individual to individual. Others are inoculated into animals directly through wounds, as in the case of rabies, vaccinia, et cetera. And, lastly, there are also those which are transmitted by insect carriers, examples of this type being yellow fever, dengue, papataci fever, et cetera.

In giving you this rather discursive story I hope I have succeeded in showing that there is a group of organisms beyond the reach of the microA new world of beings is revealed and results of greatest value to man have already been secured.

scope.

Ann Arbor, 721 Forest Avenue.

SKIN-GRAFTING.*

WALTER R. PARKER, B. S., M. D.

PROFESSOR OF OPHTHALMOLOGY IN THE UNIVERSITY OF MICHIGAN.

DEFINITION: By skin-grafting is meant the transplantation of either the whole thickness, or a portion of the superficial layers of the skin to a recently exposed or granulating surface in order to hasten its healing process, and to prevent, as far as possible, future cicatricial contraction.1

Grafts may be divided in general into thin grafts, where only a portion of the thickness of the skin is utilized (Reverdin and Thiersch), and thick grafts, where the whole thickness of the skin is used (usually spoken of as Wolf grafts).

Thick grafts may or may not be pedunculated. The pedunculated grafts may be from the immediate neighborhood, swung into place without disturbing the peduncle, or transplanted from distant parts, leaving the peduncle attached until the flap becomes viable, when it is cut from its base.

Thin grafts may be small or large, varying in size from a millimeter in diameter to several centimeters square.

Grafts may be obtained from the same person (autodermic); from another individual of the same species (isodermic); or from a lower species (zoodermic). The majority of grafts are taken from the same. individual, although they may be taken from amputated limbs and cadavers within a few hours after death due to accident.

(a) ZOODERMIC: Zoodermic grafting has been tried for years with more or less success, grafts having been taken from the inner surface of a pullet's wing, skin from pigeons, young puppies, guinea-pigs, rats and rabbits. My own experience has been limited to the transplantation of the conjunctiva of rabbits to the human eye. All were unsuccessful.

Miles, who has transplanted the skin of dogs, rabbits, kittens, and frogs, was most successful with grafts from dogs and least successful with frog's skin.

Davis has taken whole-thickness grafts without the subcutaneous fat from the abdomen of young fox terriers and transplanted them on patients. with ulcers following burns, and found that in most cases they would take, but that they macerated very easily.

Reverdin usually obtained his small bits of epidermis from the inner surface of the leg. He held the skin tense over the flat surface of the tibia and introduced the point of a rather large venesection lancet to the depth of five millimeters, then pushed it forward so that the point should emerge three or four millimeters further on, the small piece of epidermis being cut loose by the edges of the lancet. He placed the lancet bearing the graft upon the healthy granulations and slid it off, raw surface down, taking care that the edges were not rolled under.

Agnew transfixed a bit of the superficial layer of the skin with a sewing needle and raised it in the form of a cone, then with a razor or *Read before the Clinical Society of the University of Michigan, June 7, 1911. 'I quote from a monograph on "Skin Transplantation," by John Davis, M. D., Johns Hopkins Reports, Volume XV.

sharp scalpel cut off the top of the cone and transferred it on the needle to the desired point. Many points may be transplanted by this method, numbering in the thousands. There is more liability of cicatricial contraction following this method than when the larger grafts are used.

Thiersch grafts are those most commonly used and are of enormous size in comparison to those advocated by Reverdin. Thiersch's original instructions in 1886 were to cut or scrape off the granulations down to the firm underlying tissue and to stop all hemorrhage. The skin to be grafted was removed from the outer surface of the upper arm, which was put on and stretched with one hand, while with a razor very thin films of skin are cut by a sawing motion. He held that even the thinnest films obtained in this way contained in addition to the superficial epidemis, the papillary layer as well as a portion of the reticular layer of the corium. He was able to cut and successfully transplant pieces two by ten centimeters. He thought it necessary to transplant directly on the firm base and not on the unstable soft granulations.

Socin, in 1888, used a microtome knife for cutting these grafts and thus was able to obtain larger, broader films. Thiersch considered this a distinct advance in technic.

The Thiersch method is the method of choice, on account of its simplicity and smaller operative action, but in such exposed localities as the elbow, palm of the hand, and the knee, where there is considerable pressure and friction, whole-thickness flaps are better. It is advisable to use large flaps, as the healing is as good as with small ones and there are fewer scars and therefore less likelihood to future contraction.

The skin may be taken from almost any situation where there is sufficient laxity of tissue to admit of suturing of the edges of the fresh wound, the selection of location being determined by the nature of graft desired. Sessile flaps have been successfully placed on healthy tendons, fascia, muscle, spongy bone, and periosteum. According to Krouse, the ideal results to be obtained, namely, elasticity, softness, movability, and normal color, can be obtained in about one-third of the full takes In whole-skin grafts a brown pigmentation may appear which, according to Krouse, originates from the broken down hemoglobin of the blood which remains in the flap. This can be guarded against by squeezing the flap gently between pieces of gauze before applying. This discoloration is unimportant in the covered portions of the body, but is much more serious on the face for cosmetic reasons. Full-thickness flaps sometimes shrivel, due probably to the puckering of the scar tissue in the depth of the wound. While these changes in no way impair the efficiency of the flap, nevertheless they would prevent us, except in cases of necessity, from using sessile flaps on the face, pedunculated flaps and Thiersch flaps being best for this region. Before the technic of full-thickness sessile flaps was perfected and proved so successful, better results were obtained by living, pedunculated flaps with subsequent amputation of the pedicle. The ordinary transplantation from distant parts can be used in comparatively few cases, the forced position being very trying to the patient, and in addition a considerable defect is left.