cytes in passive hyperæmia, frogs were curarized, the femoral vein. exposed by dissection, and pressure applied by means of an India rubber band and a plug of cork. The web of the corresponding foot was stretched upon the stage of the microscope, and the pressure upon the vein regulated so as to retard the current of blood without producing complete stagnation. That the effects produced were due to passive and not to active hyperæmia, to mechanical congestion and not to inflammation, is shown by the absence of other phenomena of inflammation, and by the fact that discontinuance of the pressure on the vein was immediately followed by full restoration of the circulation. In one instance, migration was observed within three hours after compression was made, but in others no migration was detected within the first nine hours. Sooner or later, in all cases, leucocytes were seen to leave the vessels in considerable numbers, not usually from the minutest capillaries but from the large capillaries and small veins of from 100 to reo of an inch in diameter. Emigration also occurred where the currents were rapid and sparsely supplied with corpuscles, as well as from slow currents crowded with corpuscles. The time of exit averaged from one to two hours, but was sometimes as short as twenty minutes. The method of locomotion did not, of course, differ from that exhibited in inflammation, though excessive change of form, and protrusion of long processes, was not noticed. Frequently a leucocyte flattened against the wall, then a bud appeared external to the wall, and the intra-vascular portion gradually shrank away as this bud increased in size. Often the locomotion was continued after the leucocyte had wholly left the vessel, so that it traveled several times its own diameter from the place of exit. Other corpuscles, too, were prone to pass out at the same point, so that sometimes several would be crowded together within the vascular wall, and an hour later would be in close proximity external to the vessel opposite the same point. Certain red corpuscles of the same shape and size, and without a nucleus, but of unmistakably red color, were frequently seen to migrate in a similar manner, and to such an extent that after thirtysix hours there were many patches in the field which looked almost like hemorrhages. That they were not hemorrhages was inferred, because many of them had been seen to migrate, because they were fixed in the tissue, and not floating in the blood serum, and because they were all small and round, and different from the large, oval, nucleated red corpuscles of the animal experimented upon. This behavior of the small red corpuscles exhibits a close relation with the white, and furnishes another link in the chain of circumstantial evidence that the red corpuscles are transformed white ones. The facts observed would seem to favor the theory that the migration is a simple filtration of colloid substances, from increased blood pressure and diminished blood velocity, rather

than an active movement due to their "glutinosity." How far these facts account for the connective tissue hyperplasia which accompanies varicose veins, the enlargement of the spleen which usually follows portal obstruction, etc., depends upon one's ideas of pathogenesis.

"A Handy Rule for use in Micrometry," by C. M. Vorce, of Cleveland, described very clearly the methods adopted by the author in making miscropical measurements.

Professor Romyn Hitchcock, of New York, in a paper entitled, "A Standard Micrometer," urged the adoption of a standard which should give some uniformity in micrometric work by different observers. Efforts to secure this end have been made, years ago, but they seem to have led to no results. We are now as far from a definite standard as ever, and the question can only be settled by a representative body like this, or by one convened for the special purpose. Not only accuracy but uniformity is essential, for convenience in reading and comparing observations. A fraction of an inch might seem the preferable unit of measurement to us in this country, but it can never become universal. The metric system is the only one that can ever become universal, and we should now adopt it even at some temporary sacrifice of convenience.

Professor Rogers, whose facilities for accurate ruling have been greatly increased during the last few months, proposes to rule six scales, as nearly alike as possible, and donate five of them to the same number of microscopical societies, as standards, the societies having first appointed a committee to examine, compare, and approve the scales. (Near the close of the Congress, resolutions were offered by Professor Hitchcock, and adopted, recommending 1 of a millimetre as our unit of micrometry, requesting microscopical societies to formally adopt this standard, and recommending to the favorable consideration of the societies, Professor W. A. Rogers plan for the acquisition and distribution of standard scales. This action was taken by the Congress without opportunity for discussion, and for the purpose of bringing the matter before the country for concerted action. It is possible that the unit suggested will need reconsideration, as one millimetre might be more convenient and more easily agreed upon than a nameless fraction).-(To be Continued.)

EXCHANGES.-Lake Michigan diatoms, mounted or raw material, also diatoms of Northern Illinois, for good slides or material. B. W. Thomas, 132 La Salle street, Chicago, Illinois.

Diatoms: Rhabdonema adriatica, Synedra ulna, splendens and superba, Tabellaria flocculosa, Fragilaria virescens, Isthmia nervosa, diatomaceous earths and other unmounted material, for named diatoms or other good mounted objects. M. A. Booth, Longmeadow, Mass.

Slides of named diatoms, also peristome of Funaria hygro

metrica, offered in exchange. Jos. McKay, 24 Liberty street, Troy, N. Y.

A variety of interesting objects from the Bahamas, mounted or unmounted, for exchange. C. C. Merriman, Rochester, N. Y.

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SCIENTIFIC NEWS.

-We learn from the parties in the field in the Yellowstone National Park, that the work of Prof. Hayden's United States Geological Survey of the Territories has progressed most favorably despite the unsettled nature of the country, owing to the Indian troubles. The general features of the park have been exhaustively surveyed, an enormous amount of material in the morainal deposits and especially the structure of the Wind River mountains.

Meanwhile the reports of the survey, and particularly the Geological map of Colorado lately issued by this Survey, are winning golden opinions in Europe. A gentleman writes us from Paris as follows: "The Hayden Survey is popular in both England and France. I repeatedly heard expressions of regret that there should be any disposition to hamper or oppose it in any way. Such opposition would be looked on here as springing, without doubt, from unworthy motives." An elaborate notice by Mr. Oldham, the late distinguished director of the Geological Survey of India, appears in the Geological Magazine, in which the highest praise is given to the work. That all Americans should take pride in this great work and others of the kind, is made apparent by the favorable notices which have appeared in European journals. In letters lately received at the office of the survey, Prof. Andrew C. Ramsay, the veteran director of the Geological Survey of Great Britain, writes: "I have to-day received a copy of your Colorado Atlas, for which I am exceedingly obliged. I have all the maps, etc., spread out on one of the large drawing tables in the geological survey office, and have had a long look at them. The beauty of the engraving and coloring is most remarkable, and quite astonished me. I know nothing of the kind superior, or even equal to this work, especially when we consider the physical character of the country and the hardships that such a survey must entail. That so much has been done, and done in such a manner, speaks volumes for the energy and skill of you and all your men, and it is a credit to any government to have been the means of producing such a masterly piece of work."

Prof. Archibald Geikie, director of the Geological Survey of Scotland, writes: "Your magnificent Atlas of Colorado has just come. I have had time merely to look over the maps and sections in a cursory way. But I cannot delay to send you a few

lines of the heartiest congratulation on the completion of this most splendid contribution to science, and to the opening up of the resources of your great country. I shall take an early opportunity of going quietly over the maps and of speaking publicly about them. The care and elaboration of the original field-work, and the beauty of the execution of the plates, combine to make this atlas a national work of which any government might justly be proud."

We sincerely hope that Congress will certainly not decrease next year the amount of the annual grant for a survey, which, without disparagement to any other, has been conducted in such a broad as well as prudent spirit as to win golden opinions from those best qualified to judge of the manner of conducting such a survey.

Prof. Cope has purchased the collections of vertebrate fossils exhibited by the Argentine Confederation at the Exposition of Paris. The collection embraces those of three exhibitors, and is one of the most extensive which has ever left Buenos Ayres. It includes 75 to 100 species, which represent all the more important types of the Pampean formation. There are twelve species of Glyptodon, and nineteen nearly complete skeletons of various forms. The most beautiful of these is that of a Macharodus similar to the Brazilian species. Prof. Cope retains a series of duplicates, some of them entire skeletons, for sale.

- NOTICE. Having removed from Salem to Providence, R. I., the editorial office of the AMERICAN NATURALIST will be at the latter address, where all exchanges, articles, letters, and specimens designed for the editors may be sent. A. S. PACKARD, JR.

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PROCEEDINGS OF SCIENTIFIC SOCIETIES.

SAN FRANCISCO MICROSCOPICAL SOCIETY.-The regular meeting was held July 11th. Of the business routine the most interesting part was the announcement of several donations and purchases for the library and cabinet. Rev. Mr. Bleasdale generously completed the suite of Dr. Carpenter's slides, already numbering eleven, by an addition of three more-shell sections of Unio occidens, Anomia ephippium and Terebratula ampulla.

The California State Geological Society presented specimens of "diatomite," from Santa Barbara, a flinty mineral supposed to have been deposited from silica-impregnated waters passing out

of a diatom earth, and Mr. Hanks sent some lichens containing diatoms from a parapet of the Palace at Versailles.

After examining the beautiful slides of foraminifera, mounted by Mr. Merriam and exhibited by President Hyde, the members began their contributions to the topic of the evening, "The microscopical examination of sea water, with reference to its animal and vegetable forms." Dr. Whitney spoke at some length of his physical and chemical investigations upon Pacific ocean water, taken at insetting tide just within the Golden Gate. He spoke of the lime and silica in solution in sea water, and beside attributing to these the origin of the foraminifera shells and diatom frustules, a well-known fact, spoke of the silica in solution as a probable source of sand, since he considered the fine deposit that gradually fell in his jars of sea water as coming from solution, and not as a long suspended silt, the view generally held.

After selecting for the next topic "The Lower Forms of Marine Life," the society listened to a translation, by Secretary Clark, of a short paper on "The Alternate Generation of the Echinodermata," by Prof. Haeckel.

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE.The next meeting is to be held in Saratoga on the last Wednesday of August, 1879. The officers elected for that meeting are Prof. G. F. Barker, of Philadelphia, president; Prof. S P. Langley, of Alleghany, Pa., vice-president of section A; Major J. W. Powell, vice-president of section B; Prof. Ira Remsen, chairman of subsection of chemistry and Prof. E. W. Morley, of Hudson, Ohio, chairman of subsection of microscopy. Among the noteworthy papers in geology and biology were those by C. O. Whitman on the Embryology of Clepsine, Prof. I. E. Todd's on Richthofen's Theory of the Loess in the light of the deposits of the Missouri, A. G. Weatherby's Are the so-called Chatetes of the Cincinnati Group Bryozoans? and his remarks on the Geographical Distribution of the land and freshwater Molluscs of the United States and their local varieties. Major Powell spoke on the rainfall of the arid region of the United States, while Prof. B. G. Wilder made a communication on a remnant of the spiracles in Amia and Lepidosteus, and S. A. Forbes read a paper on the development of Amia, Mr. C. E. Dalton made a communication on the geological history of the Colorado river and plateaus, and Mr. A. Lakes spoke of the discovery of Atlantosaurus and other Dinosaurs in the Rocky mountains of Colorado. The anthropological papers were noticed in our last number.

BOSTON SOCIETY OF NATURAL HISTORY, Oct. 2d.-Mr. W. O. Crosby read notes on the physical geography and geology of Trinidad.