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piece about three inches long is cut out from the centre of the slide, which contains the pinion. A small piece is cut off from the end of this piece, so as to allow a motion of about an eighth of an inch. A strong spiral spring is placed above this to keep it pressed down to the bottom of its slot. It can be raised by a lever which is acted upon by the milledhead of the fine adjustment. By turning this screw the lever acts upon the piece containing the pinion and moves it, and with it also the tube. The milled-head is provided with an index and subdivided in such a way that turning the screw past one division will move the tube onethousandth of an inch. The usefulness of this device is still further increased by a scale subdivided into

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deep groove to receive the rack; the sides of this groove are undercut with secondary grooves at right angles with the first.

A rib considerably longer than the slide on the limb is attached to the tube. This rib fits upon the slide; from its centre projects a secondary rib, which bears the rack. On each side of the rib which holds the rack are two small ribs, which fit into the V-shaped grooves of the slide; they are the bearing surfaces of the tube. From each side of the secondary rib which carries the rack, project two flanges, which fit into the under-cut grooves in the deep groove in the centre of the slide. Their purpose is to keep the small ribs closely applied to the V-shaped grooves.

The fine adjustment is behind. A

160°

FIG. 2.-STAGE OF THE 'CONGRESS" STAND.

hundredths of an inch, attached to the limb where it joins the tube.

With a magnifying power of about 2,000 diameters used on this stand, there is not the slighest apparent displacement of the object by any motion of the fine adjustment, and the working of the screw-collar, is accomplished with the greatest ease.

The nose-piece carrying the Wenham prism is readily removed and another one substituted having no diaphragm.

The substage and mirror are attached to bars, both of which swing on a pivot around the object as a centre; they both have a silvered and graduated limb, and can be swung together or separately. When these two bars are brought together they are held by a spring stop; another spring stop indicates when they are brought to the centre.

By

The swinging substage may be used for measuring the angular aperture objectives. This method consists in attaching a small lamp to the substage and using it as a source of light for observing some object upon the stage of the microscope. gradually swinging the substage and lamp until the image disappears, we have measured all the usable angular aperture of the objective. The substage is moved up and down upon its bar by a rack and pinion, as usual. Its centering arrangement is placed behind the ring, and consists of a rack and pinion, and a screw similar to the movement of most mechanical stages. It has a motion from side to side of about half an inch, and a quarter of an inch forward and back. An arm beneath the stage holds the hemispherical lens or Woodward prism. This arm can be removed. The lens or prism can also be placed in the substage. In the latter they can be centered with great ease. Below the substage is a ring to hold the polarizer. This ring swings to one side, enabling the observer to examine an object alternately with polarized and unpolarized light, without trouble or disturbing the object.

The stage is held by a saddlepiece which is steadied by a strong brace passing down from the limb. It is entirely independent of the swinging of the mirror and substage. This saddle-piece contains a set of screws with perforated heads for centering the ring which supports the stage. By removing these screws so far back the ring can be very much reduced in thickness without impairment in strength or stiffness. The stage rests upon this ring. It rotates and can be centered with the greatest exactness by the screws in the saddlepiece.

The stage is a revival of an idea which Mr. Bulloch says was applied by Spencer thirty years ago. It consists of the ordinary stage-plate, having in its centre a large square hole. One side of this plate contains a wide dove-tailed groove. In this groove slides a bar with its surface level with the top of the plate. At right angles to this bar is attached another bar. On this second bar slides a third bar, into which it has been dove-tailed. The motion of this third bar is, of course, at right angles to the motion of the first. A thin plate is attached to the third bar and lies flat upon the stage-plate. This plate is perforated and holds the slide by means of a spring. It will be seen that this arrangement permits of motion of the thin plate in two directions at right angles to one another. Two pinions, perpendicular to the stage, which work one through the other, and act upon racks placed at right angles, effect this motion. Scales placed at right angles serve the purpose of finders.

This form of stage presents several advantages. It is convenient. The perpendicular milled-heads of the stage-motion are within easy reach of the hand, and from them a change can be made to the milled-heads of the coarse or fine adjustment, without thought or trouble.

The motion of the stage is very easy and rapid; an animalcule can

be followed, however swift or tortuous its course may be. It permits a complete rotation. There is no machinery underneath to interfere with the course of the light. The stage may be made extremely thin. In this stand light may be admitted at an angle of something more than 160 degrees.

The stand has also an arrangement for drawing, suggested to Mr. Bulloch by Dr. Lester Curtis, which is designed to do away with some of the difficulties attending the use of the ordinary camera lucida. A little table is fastened to the limb by milled-head screws. Paper is placed upon this for drawing. One of Hartnack's rightangled camera lucidas is used. Drawing can be done in any position of the microscope. There is hardly more preparation required for this than would be required to change an eyepiece. The comfort of this arrangement, when one is doing work which requires much drawing while observation is going on, needs to be experienced to be appreciated.

Large vs. Small Stands.

I must thank you Mr. Editor, for your criticism of my remarks on stands in your November number. You have undoubtedly done the best you could for your side of the question, and that is very little. As the matter is one of the first importance to all investigators, as well as to those who are to be the investigators of the future, I must ask the privilege of criticizing my critic, and allow me to remind you that this is not a new subject with me; I fought the same battle with Prasmowsky in the Lens several years ago.

You now ignore the main question which I endeavored to make prominent: There can be no doubt that the time of large and costly microscopes is passed. Indeed, there will be always some that will want them, but the experienced worker, whether he

be an amateur or a professional, will surely discard them."

It is this teaching that I reject, and claim ought to be rejected; and I claim also that it is rejected.

Now I know that there are persons, not only in Europe, but in America, who think and talk as you do; but I do not know that any one of them has any experience of the difference of vision between the common German model and the full-sized teninch tube of English and American instruments. As I said before, the whole use of the microscope is to see with, and considerations of cost or convenience must be secondary to seeing best. It does not follow that the full-sized Jackson model should be very costly, further than two pounds of brass cost more than one pound. Of course, some persons need or wish for, appliances that cannot be used at all, or not efficiently on the short stands. That is another matter, I am claiming the time of large microscopes is not passed.

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I utterly deny that the small stands are more convenient." Any use of a microscope is a matter of delicate manipulation, and it is equally convenient to take a sixteen pound microscope from its case, where it stands vertically ready for use, as it is a four pound one.

You say, "We have in no place especially commended the German model, but we wrote of 'low stands not much higher than the German model.'" Precisely that I, and I presume every one, understands to be a commendation of the German model, and my objection is not especially to German, but to any not much higher.

My omission in the quotation that you refer to, was intentional; I was not, in that passage, considering the minor question of convenience, but the great all-important one of superiority of vision which, practically you surrender.

To conclude, if any yet claims that the time of large microscopes-mean

ing by "large," ten-inch tubes and ten to sixteen pounds weight "has come," let them accept my proposition of the demonstration of superior optical performance, or forever after hold their peace.

The question is not for argument, but one of fact.

CHARLES STODDER.

Cleaning Diatoms.

I offer the following suggestion for cleaning diatomaceous material when largely contaminated with sand. A quantity of the material is placed in a teaspoon, and water is then added until the teaspoon is nearly filled; the spoon is gently shaken with a back and forth or a circular motion, for a few seconds or longer, when the water must be quickly drawn off by applying the tip of a finger to the point of the spoon, taking care to draw off the superficial water, without allowing the heavier sediment to pass over the point. Pour from the spoon into a watch-glass, the surplus water is then drained off, and the diatoms removed for mounting. This method produces a magical concentration of the diatoms, large and small, making the remaining sand inconspicuous by the superabundance of the diatoms.

K. M. CUNNINGHAM.

EDITORIAL.

Subscriptions.-Remittances for subscription should be made by post-office money-order, by drafts payable in New York, or in registered letters. Money sent in any other way will be at the sender's risk.

A receipt will be immediately given for money received by open mail.

BOSTON WATER.-The report of Prof. Ira Remsen on the Boston water, referred to last month, has been published by the city of Boston. It is illustrated by a colored plate representing the fresh-water sponge, Spongilla fluviatilis, with a transverse and a longitudinal section of the sponge. A letter from Prof. Farlow

is also printed, who expresses his belief that the "cucumber odor" is not due to any vegetable growing in the water. Prof. Remsen's conclusions, which were quite fully stated in our December number, were combated by a number of gentlemen at a meeting of the Boston Society of Natural History, but we are still inclined to the belief, after carefully reading his official report, that they will be verified by future investigations.

MICROSCOPICAL SOCIETIES.-We have heretofore followed the established custom of publishing the reports of microscopical societies as they have been furnished by the secretaries, omitting matters of a purely business nature, or such as were only of local interest. This course has, for various reasons, been more or less unsatisfactory; for we have felt that the space occupied by the reports, while too small to admit of full notices of the meetings of all societies, could be filled with matters of greater general interest and importance if the reports were condensed and given in a different form.

We have, therefore, decided to adopt a different plan this year, which, although it will add to the labor of editing the JOURNAL, will, nevertheless, we believe, prove more satisfactory to subscribers and also to the members of the societies.

We propose to take the reports of meetings that may be sent to us each month, read them carefully, and embody the most instructive and interesting features of them all in a single article, as in this number. This plan will doubtless make the reports more readable, and it will afford us an opportunity to offer occasional suggestions and criticisms. Under the former plan we were occasionally obliged to print erroneous observations or conclusions without comment, we can now indicate these without offence to the authors, for even the best of us are liable to make mistakes, and we have not the slight

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Thus, then, it becomes possible to affect sheep and cattle with a form of anthrax-disease so mild as to bear much the same relation to the severer forms that cow-pox bears to small-pox; and for this artificial affection with the mitigated disorder, Pasteur uses the term 'vaccination.' The question that now arises-to which the whole previous investigation has led up is the most important of all: Does this 'vaccination' with the mild virus afford the same protection against the action of the severe, that is imparted by cow-pox vaccination against small-pox? To this question affirmative answers were last

teur predicted that on the following day the twenty-five sheep inoculated for the first time would all be dead, while those protected by previous vaccination with the mild virus would be perfectly free from even slight indisposition. A large assemblage of agricultural authorities, cavalry-officers, and veterinary surgeons having met at the field the next afternoon (June 1st), the result was found to be exactly in accordance with M. Pasteur's predictions."

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CONTAGIOUS DISEASES OF ANIMALS. Special Report No. 34 of the Department of Agriculture, contains several valuable contributions to the knowledge of diseases of animals, to which we cannot do justice in the space at our disposal. However, some of the investigations recorded in the report deserve especial mention here; among them those of Dr. D. E. Salmon, on swine-plague and fowl-chol

After recording some experiments upon the efficiency of certain disinfectants in destroying the virus of swine-plague, some microscopical investigations in regard to the nature of the virus are quite fully detailed.

era. obtained by Professor Greenfield (on Professor Burdon-Sanderson's suggestion) in regard to bovine animals, and by M. Toussaint in regard to sheep and dogs; the former, when vaccinated from rodents, and the latter from fluids cultivated outside the living body after a method devised by M. Toussaint, proving themselves incapable of being infected with any form of anthrax-disease, though repeatedly inoculated with the malignant virus, and remaining free from all disorder, either

constitutional or local. The same result having been obtained from experiments made by Pasteur himself, probably about the same date, with charbon-virus cultivated in the manner previously described, it was deemed expedient by one of the Provincial Agricultural Societies of France that this important discovery should be publicly demonstrated on a great scale. Accordingly, a farm and a flock of fifty sheep having been placed at M. Pasteur's disposal, he vaccinated twenty-five of the flock (distinguished by a perforation of their ears) with the mild virus on the 3d of May last, and repeated the operation. on the 17th of the same month. The animals all passed through a slight indisposition, but at the end of the month none of them were found to have lost either fat, appetite, or liveliness. On the 31st of that month, all the fifty sheep, without distinction, were inoculated with the strongest charbon-virus, and M. Pas

Dr. Salmon finds a Micrococcus in the blood of animals affected with swine-plague, which he regards as the possible cause of the disease. However, the precise relation between the disease and the organisms referred to is clearly stated as follows, quoting from Dr. Salmon's report:

"If, in conclusion, we admit the presence of a particular bacteria-form in the effusions, or even in the blood, in the disease, the facts already referred to in regard to the presence of such organisms in non-contagious maladies, often before death, renders it necessary that a connection be established between such bacteria and the contagium; certainly no satisfactory connection or identity has been shown to exist between the bacteria and virus in this disease up to the present time."

There are many interesting observations described in this report, and

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