REPORT OF THE MICROSCOPIST. SIR: I have the honor to submit herewith my twentieth annual report as chief of the Division of Microscopy. The work done during the past year relates in a great measure to the microscopical investigation of food adulterations, food fats and oils, textile fibers, and edible and poisonous mushrooms. In relation to fiber investigations, I have had constructed, with your permission, a new machine of my invention for determining the general value and tensile strength of farmers' binder twine and for other purposes connected with farming interests. In these tests I have been courteously assisted by the officer in charge of the Bureau of Equipment of the Boston Navy-yard, and also by Mr. E. B. Balch, superintendent of the National Cordage Company, New York City. This machine is now in good working order. A number of experiments have been made with it, and the results of the preliminary trials are herewith furnished. It may be well to state here that this machine has no relation to another machine invented by me and illustrated herein, designed solely for testing and comparing the relative strengths of fibers and of threads. There is also furnished in this report an interesting statement of preliminary tests made with this machine of four samples of foreign flax, showing their relative strength as compared with their relative cost per ton. These samples of flax were received from Mr. J. M. Anderson, Belfast, Ireland. During the past year I have also devoted considerable time to investigating and reporting upon wool fibers, and have testified officially in the United States courts, for the Secretary of the Treasury, in cases where such examinations were pertinent to a question of dutiable merchandise. Valuable samples of foreign and native wools have been added to the collection in this division through the courtesy of Mr. E. A. Greene, Philadelphia, Pa.; also of Mr. John Consalus, Troy, N. Y., and others. It may also be proper for me to mention that I have in progress the preparation of a large collection of models representing, by casts taken from nature, the edible and poisonous mushrooms of the United States, in groupings and otherwise, illustrating their manner of growth, development, coloring, and as far as possible their diversity of habitat. In this line of work enough has already been done to shape roughly an exhibit for the World's Columbian Exposition, which exhibit, it is desirable, should be as comprehensive and perfect as the one in the museum at Nice, France, which shows the mushrooms prepared in plaster, life-size, and colored after nature. In this way the public is enabled readily to compare one kind of mushroom with another, and to study them in all their stages of growth. With the approval and coöperation of the Assistant Secretary, I have, as already said, commenced my preparations for such an exhibit, which will be made as complete as the means placed at my disposal will per mit. In consideration of the many requests received during the past year for such information as would enable one skilled in the use of the microscope to distinguish pure lard from fictitious lard, I have prepared a preliminary statement of experiments for those who desire to make microscopic observations in this line of research: (1) Heat, over the flame of a Bunsen burner, in a porcelain capsule, 4 ounces of pure home-rendered leaf lard, for a period of one minute, and allow it to cool slowly until it solidifies, which will require a period of about four hours, in an atmosphere of about 75° F. The crystalline groupings of this sample will appear very small when viewed under a power of 100 diameters. (2) Prepare, in like manner, another sample of pure leaf lard, heating it for a period of four minutes, and allowing it to cool slowly, as above. It will be observed that pure lard in this case shows well-defined crystals of stearin, viewed under the microscope as above, and will, without regard to the high temperatures to which it has been exposed, consolidate in about the same time as that given in the first experiment. (3) Prepare a sample of compound lard consisting of commercial stearin and sufficient cotton-seed oil to bring the stearin to the consistency of good pure lard; heat four minutes, and allow this mixture to cool slowly as above. It will consolidate in about an hour at 75° F. (4) Prepare a second sample of compound lard, consisting principally of commercial stearin to which a trace of pure lard has been added; heat this compound for a period of four minutes. This compound will also consolidate quickly, owing to the presence of stearin in large quantity. (5) Prepare a third sample of compound lard, consisting of commercial stearin, oleo, and cotton-seed oil, with a trace of pure lard; heat four minutes, and allow it to cool slowly, at 75° F. In this case it will be observed that the time required for consolidation will depend upon the amount of stearin present. (6) Prepare a sample of commercial oleo after the method of the first experiment. This, like pure lard, will require about four hours, at 750 F., to consolidate. (7) Prepare a sample of commercial stearin, heating it four minutes. This will consolidate in about half an hour or less, at the temperature given above. Some samples of compound lard are very deceptive in appearance, being smooth and translucent, especially such as are composed of lard and oleo, but these are easily detected by the use of the microscope and polarized light. My usual practice is, first, to examine each sample with the unaided eye, compressing a portion of the lard about the size of a large pin-head between two pieces of clear glass about one inch square each, and holding each sample up to the light to compare it with a sample of home-rendered lard similarly prepared. As fictitions lard contains a large amount of stearin, it will exhibit by this method of examination many white spots, which represent the crystallized stearin, and which are not seen in pure lard. The amount of natural stearin in pure lard is so small that it is not visible to the unaided eye by this method of examination; therefore the microscope should be used in the examination of pure lard, as the groupings of the crystallized fats of |