The following very great modification of the method proposed by Ranvier, in his treatise on histology,1 has been in uge for some time in the Anatomical Laboratory of Cornell University, and has given uniformly excellent results. Preparations made three years ago are quite as good as at first.

Three or four drops of fresh blood are allowed to fall into 10 cc. of normal salt solution (common salt 750 milligrammes, water 100 cc.), preferably contained in a high narrow vessel like a graduate glass or beaker. The mixture of blood and salt solution should be well agitated and then 100 cc. of a saturated aqueous solution of picric acid added with constant stirring. After the corpuscles have settled, as much of the supernatant liquid as possible is poured off, and in its place is put about an equal volume of normal salt solution. The corpuscles are allowed to settle, the liquid poured off and another volume of salt solution added. This is continued until the salt solution acquires only a faint yellow tinge.

The use of the salt solution is, first, to dilute the blood in order to avoid distortion of the corpuscles, and second, to wash away the picric acid so that the subsequent staining will be more satisfactory.

After pouring off the last salt solution, there is put in its place 10 cc. of a mixture of five parts of Frey's carmine and ninety-five parts of picrocarmine. The corpuscles will stain in from one to fifteen hours. A drop of the agitated mixture should be examined occasionally to ascertain when the staining is sufficient. The nucleus should be deep red, and the body of the corpuscle yellow or pinkish.

When the staining is completed, as much stainer as possible should be poured off, and replaced by 10 or 15 cc. of acid glycerine (glycerine 100 cc., acetic or formic acid 1 cc.). This mixture of corpuscles and glycerine may be placed in a bottle and used at any time, it being simply necessary to agitate the mixture slightly or to take up some of the sediment with a pipette and mount it precisely as any other glycerine preparation.

Summary.-1. The fresh blood is first diluted with about fifty times its volume of normal salt solution.

2. To this diluted blood is added ten times as great a volume of a saturated aqueous solution of picric acid.

Traité technique de Histologic, p. 195.

3. The picric acid is washed away with normal salt solution. 4. The corpuscles are stained with picrocarmine, or a mixture of this and Frey's carmine.

5. They are preserved in acid glycerine, and may be mounted for the microscope at any time.

METHOD OF PREPARING AND MOUNTING WINGS OF MICROLEPIDOPTERA. By C. H. FERNALD, of Orono, Me.

FOR a long time I have been seeking some method, by means of which, the wings of the microlepidoptera could be prepared, so that the venation could be studied under the compound microscope, in a manner that would leave no doubt of the presence, or absence, of the faintest vein in the whole wing-structure.

The removal of the scales by mechanical means, as resorted to by some, was to me quite unsatisfactory, and, in some cases, even impracticable. I therefore tried some of the methods recommended for bleaching the wings of small moths. That described by Chambers, in the Canadian Entomologist, was not a success in all cases, but whether not properly tried, I cannot say.

I next tried the method for bleaching the wings, published by Dimmock, and while this seemed to be a success so far as the bleaching was concerned, the final mounting did not always give satisfactory results; for when mounted dry, the scales, although bleached, were not sufficiently transparent to show clearly the more obscure parts of the structure, and when mounted in Canada balsam, the entire wing was rendered so transparent that only the larger veins were visible, and I found it extremely difficult to get rid of the air bubbles, which so readily gathered under the concave portions of certain minute wings.

I next tried mounting in cold glycerine. After having been bleached by Dimmock's method, the wings were transferred to the slide direct from the water in which they were washed, then allowed to dry, which was sometimes hastened by holding the slide over the flame of a lamp. When quite dry, a drop of glycer ine was added and the cover at once put on, and where the

glycerine penetrated around the edges so as completely to saturate portions of the wing, the scales at once became transparent and the structure was clearly apparent.

The difficulty still remained to replace the air under the concave portions of the wing with the glycerine, so that it could come to, and completely saturate, every portion of the wing, to the exclusion of all the air. Recourse was now had to heat, and by holding the slide over the lamp till ebullition took place, the glycerine was found to replace the air without any injury to the wing structure, and even in those refractory cases where the glycerine was allowed to boil for a considerable length of time, no injury whatever was done to the wing-membrane.

THE MICROSCOPICAL INVESTIGATIONS OF THE HAVANA YELLOW FEVER COMMISSION. BY GEO. M. STERNBERG, of Washington, D. C.

THE purpose of the present paper is to give a general idea of the nature and objects of the investigations in which the writer has been engaged during the past year, under the auspices of the National Board of Health, and, more especially, to bring to notice the results obtained in photographing minute organisms, and to call attention to the great value of this method in conducting similar investigations.

A photographic memorandum of an object which we have seen under the microscope, while it may not be so sharply defined as a drawing, has the advantage of being quickly made, and is an unimpeachable record of what has been seen. A record, it is true, which conveys but little meaning to the untrained eye, just as a dingy painting, by one of the old masters, fails to tell its story to the eye of an untutored savage; but which, nevertheless, is full of meaning and of interest for the skilled microscopist. The photograph also saves great time and labor in the measurement of objects, and makes it easy to compare objects seen at different times and places by different observers. It may also be duplicated indefinitely; and when everything is working well, fifteen or

1 Surg. U. S. A., Secretary of the Commission.

twenty negatives may be made, with the assistance of a skilled photographer, in the time which would be required by an accomplished draughtsman to make a single copy of any one of them. Many of my photographs have been made from extemporaneous preparations, in which a delay of half an hour or less, for the purpose of making drawings and measurements, would have resulted in the destruction of the specimen by drying of the liquid in which it was immersed.

All microscopists in the habit of working with high powers know how many accidents may happen to interesting extemporaneous preparations, by which the object, which has been found after a protracted search, is lost from view before the drawings and measurements desired have been made. This is obviated to a great extent by the promptness with which a photograph may be made, and with low powers we may even take instantaneous views of objects in motion. I do not claim, however, that all is plain and easy sailing and that the art of making photo-micrographs of minute objects can be acquired without effort. On the contrary, there are many difficulties with which to contend, and the chances are that the beginner will make many poor pictures and will have his temper and patience sorely tried before he attains any considerable degree of success. The labors of my friend, Surg. J. J. Woodward of the Army, have done much towards reducing these difficulties and establishing a satisfactory technique for this art, and I take pleasure in embracing the present opportunity to acknowledge my own indebtedness to him for my first lessons in photo-micrography.

As I intend to project some of these photo-micrographs for your inspection and to make a few remarks upon each, while it is displayed before you on the screen, I will not, at present, dwell npon this portion of my subject, but will proceed briefly to review the objects and results of the microscopical investigations in which I have been engaged.

The Havana Yellow Fever Commission received the following instructions from the National Board of Health.

"First. To ascertain the actual sanitary condition of the principal ports of Cuba from which shipments are made to the United States."

"Second. To increase existing knowledge as to the pathology of yellow fever."

"Third. To obtain as much information as possible with regard to the so-called endemicity of yellow fever in Cuba, and the conditions which may be supposed to determine this endemicity."

"The three points above referred to are believed to be those which will most certainly yield results to scientific investigation; and which, therefore, should receive the special attention of the Commission."

"But, in addition to these, the National Board desires that the Commission shall consider certain problems relating to this disease; problems which may be entirely insoluble, but which nevertheless, are of such importance that an effort should be made to decide whether the National Board of Health will be justified in undertaking the labor and expense which will probably be required to obtain anything like a complete solution of them, if such solution is at all possible. These problems relate to the nature and natural history of the cause of yellow fever.”

In the division of labor made by the members of the Commission, the duty of conducting the investigations under the first and third of the above headings was assigned to the chairman of the Commission, Dr. S. E. Chaillé; and that of conducting the investigations under the second heading to Dr. J. Guiteras; while my attention was chiefly given to investigations contemplated in the additional instructions:

This, then, was the task set before me: to determine the nature of the yellow fever poison; to answer the question which is uppermost in our minds whenever this disease is mentioned, and which has heretofore baffled all research. Is it an emanation from the human body? Is it a gas generated external to the body? Is it a bioplast? Is it a germ?

I might well have hesitated before undertaking this unpromising investigation, if the language of our instructions had implied that the National Board considered this an easy task, and one which they expected would be accomplished during our brief stay in Havana. But you will observe that no such result was anticipated, that the difficulty of the undertaking was fully appreciated; and that the work of the Havana Commission in this direction was looked upon as pioneer work, "to decide whether the National Board will be justified in undertaking the labor and expense which will probably be required to obtain anything like a complete solution of them, if such solution is at all possible."