instrument the tube containing the prisms may be turned to one side while the object is being adjusted upon the stage. It has also a scale, an image of which is projected upon the field of the spectrum. It has the disadvantage of being unprovided with the supplementary stage for the comparison of spectra. Messrs. R. and J. Beck of London construct a microspectroscope which is attached below the eye-piece in the position of the object-glass. This form has been highly recommended as being more simple in its arrangement and more easily manipulated, particularly in cases where two similar spectra are to be compared.

For the examination of liquids, glass cells like those shown in Fig. 11 may be employed. The form, A, is made from thick tubing like that used for barometers. About one-half inch in length is cut off, the ends ground to a square surface, and the tube cemented to an ordinary glass slide with Canada balsam. Tubes of varying lengths are convenient for

giving greater or less depth of liquid according to its intensity of color. Sorby recommends wedge-shaped cells like B. In these cells the thickness of the solution may be about one-fourth inch on one side and onefortieth on the other. The effect of varying thickness of the solution is then readily observed. The cells should have a thin cover placed over them, and be completely filled with the fluid under examination. The cover readily adheres by capillary attraction. A reduction of the amount of light transmitted through the slit is equivalent to an increase in thickness of the fluid, so that by varying the width of the opening in the stage attached to the eye-piece the spectrum is modified as much as if a change were made in the depth of liquid. Various methods have been devised for measuring the exact place of the absorption-bands. This is sometimes useful, but it is advisable in the examination of blood-stains to compare the spectrum of the suspected stain with that produced by specimens of known origin, rather than rely upon the position of the bands with reference to the projected scale, since this is liable to variation by various adjustments of the instrument.

Spectroscopic Appearance of Hæmoglobin and its Derivatives.When a concentrated solution of hæmoglobin is examined by the spectroscope, all light is excluded except the red. On diluting the solution. with water, green and blue light passes, while in the yellow and the beginning of the green portion of the spectrum a dark space makes its appearance. Still further dilution effects the resolution of this dark space into two absorption-bands near the lines D and E of the spectrum: the one nearest D is narrower, darker, and better defined than the other. The band at E has more than double the width of the other, and is somewhat weaker. These bands, called oxy-hæmoglobin bands, were discovered by Hoppe-Seyler in 1862. A proper dilution is one part of defibrinated blood in eighty parts of water viewed through a depth of one-half inch. (Pl. V., No. 1. Absorption-bands of oxy-hæmoglobin.)

If to the solution of blood-coloring matter used in the last experiment there be added a drop or two of solution of ferrous ammonium sulphate (double sulphate of iron and ammonia), or a solution of ferrous sulphate mixed with a small amount of potassio-sodic tartrate (Rochelle salt), and then a very little ammonia water, the hæmoglobin is altered chemically (deoxidized), and is called reduced hæmoglobin. An examination of the spectrum of this new product shows but one broad band in the place of the former two. This band was discovered by Stokes in 1864, and is called the reduction-band of hæmoglobin. It is also sometimes referred to as Stokes' band. (Pl. V., No. 2. Absorption-band of reduced hæmoglobin.) Agitation with air causes the two bands to reappear. The spectrum showing two bands is characteristic of arterial or oxidized blood, and the single-banded spectrum is peculiar to venous or deoxidized blood.

A solution of hæmatin in a little alcohol to which a small crystal of tartaric acid has been added shows a very broad band in the red (C), another in the green between D and E, and by very careful management of the light a third very faint band in the blue between E and F. If the solution be made strongly alkaline with ammonia the band at C disappears. The subsequent neutralization of the ammonia by acid does not restore it. These bands are called the acid and alkaline bands of hæmatin. They vary somewhat in number and position, according to the kind and quantity of acid used. (Pl. V., No. 3. The acid band of hæmatin.)

A solution of the coloring matter of blood obtained from a stain which has been but a short time exposed to the air shows the two bands of hæmoglobin, but they are weaker than is the case with fresh blood. There is also a third band in the red, near the line C. (Pl. V., No. 4. Absorption-bands of solution of blood-coloring having but a short exposure to the air.)

With a solution from blood which has been long exposed to the air the band in the red (C) is wider and darker, while the others are much weaker. (Pl. V., No. 5. Absorption-bands of blood solution after long exposure.) The addition of ammonia to such a solution causes the band in the red to disappear, but it causes the bands in the green to become much more distinct.

The effect of reducing agents added to a solution of blood obtained from a stain after prolonged exposure is shown in Pl. V., No. 6. The two bands are much darker, and perfectly well defined. They closely resemble the bands of hæmoglobin, but are a little farther to the right. In very dilute solutions the band at the right may fail to make its ap

pearance.

(Sorby, Monthly Microscopic Journal, London, vol. vi., p. 9.)

(Suffolk, Spectrum Analysis Applied to Microscopical Observation, London, 1873.)

(Preyer, Die Blutkrystalle, Jena, 1871.)

(Thudicum, Chemical Physiology, New York, 1872.)

(Rosenberg, The Use of the Spectroscope, New York, 1876.)

Crystalline Bodies obtained from Blood-Coloring Matter.-From fresh blood crystals of hæmoglobin (oxy-hæmoglobin) may be obtained which show some differences in crystalline form, according to the source whence they are derived. Blood-crystals were first observed by Funke

in 1851. (Zeitschrift fur rat. Med., vol. i., p. 148.) They may be produced from blood by mixing it with about one sixteenth its volume of ether and shaking the mixture until the liquid becomes a clear lake color. Sometimes the crystals form in a few minutes, and sometimes several days are required to develop them. A single drop of blood should be mixed with a very little ether and covered with a thin glass. Crystals are obtained less readily from the blood of the ox, pig, pigeon, and frog than from the blood of man, mouse, rabbit, and sheep; they are easily obtained from the blood of the dog, rat, squirrel, and guinea-pig. In the majority of animals the crystals are in the form of prisms belonging to the rhombic system; in the guinea-pig they are rhombic-tetrahedra, and in the squirrel they are hexagonal. They have a light-red color when observed with a microscope of low power, and appear of greater or less intensity of color according to their thickness, varying from purplish red to a peach-blossom. The tetrahedral crystals are much more soluble than those which assume the prismatic form, while the solubility of the hexagonal plates is somewhat greater than that of the prisms, but less than is the case with the tetrahedra. The general

appearance of these crystals is shown (after Funke) in Fig. 12. (Atlas de Physiolog. Chemie, Leipzig, 1853, Tl. x.) Crystals can be obtained only from fresh blood, or a moist clot not more than a day or two old. They are not characteristic of the blood of any particular genus, since all of the forms have been found in the blood of several different animals.