It will be observed, on a scrutiny of these tables, that there is a marked difference between these observers in the diameter of the corpuscles of the opossum, amounting to 1-27152d of an inch, and a similar discrepancy in those of the guinea-pig.

Prof. Formad challenges the correctness of Prof. Wormley's measurements and those of Dr. Woodward (1.3213). Prof. Formad says (Comparative Studies of Mammalian Blood, p. 18), that he examined ten different animals, making ten preparations in each case, and measuring 100 corpuscles from each animal, and found that the mean diameter was 1-3400 of an inch in every 1,000 corpuscles.

His results were confirmed by Drs. J. L. Hatch, A. J. Plumer, and Henry Wile, and by the celebrated Dr. Richardson, and they approximate nearer those of Gulliver.

Dr. Formad also says that Wormley's observations were of the corpuscles of one wild guinea-pig (cavia aperia), while Formad's examination was of the domestic (cavia cobaya), and that while Woodward's measurements were of the blood of the latter animal, that his micrometry was unreliable, in that he only examined 401 corpuscles, all from one drop of blood, and from a single individual.

I take pleasure, also, in quoting Prof. Wormley's observations of old blood stains, from his "Micrometry of Poisons," with his table and explanatory marks.

In the case of the human blood, No. 1, two months old, the deposit was in the form of a thin stain on muslin, and its nature, other than that it was mammalian blood, was unknown at the time of examination. The corpuscles were readily found, and two series of thirty corpuscles each were measured. In the human blood two and a half months old, fifty corpuscles, ranging from 1-3125th to 1-3448th of an inch, were measured.

The blood-stain of the dog, No. 6, was prepared by Dr. Frankenberg, and consisted of a single stain so minute as to be barely visible to the naked eye: its nature at the time of the examination was unknown. In this instance only fifteen corpuscles were measured.

In the ox blood four and half years old, the corpuscles were rather readily obtained,

and two closely concordant series of measurements were made.

In examinations of this kind it should be borne in mind that certain portions of a deposit may fail to yield satisfactory results, whilst from other portions the corpuscles may be readily obtained.

NUMBER OF THE RED-CORPUSCLES.

The actual number of the red corpuscles have been counted with the greatest exactness by the aid of the microscope. The method employed is very simple :

A given quantity of blood is diffused as equably as possible in a thousand times its volume of an indifferent fluid, say water. A small quantity of the fluid is then taken up in a capillary tube of known caliber, and the length of the thread of fluid estimated under the microscope by a microm

eter.

When the contents of the tubule have been thus ascertained, they are distributed upon a slide with a little solution of gum and allowed to dry. This preparation is then covered with a micrometer divided into squares, and the corpuscles in the several squares can be successively counted. This method originated with Vierordt.-(Archiv fur Physal. Hiel Kunde Band xi pp. 26, 327, 854. xiii p. 259.)

It has also been modified by Welker, who has counted the blood corpuscles of man and of various animals.-(Welker Prager Viertelgahreschrift Band xliv, p. 60. I. R. Band xx, p. 280.)

The number of red corpuscles in a cubic millimetre of blood of a healthy man is thus determined to be about 5,000,000, from which the number in a gallon, quart, pint, or ounce can be computed.

It has also been as clearly demonstrated that the relative quantity of corpuscles and plasma or serum (liquor sanguinis) in a hundred volumes of blood is thirty-six volumes of corpuscles and sixty-four volumes of plasma. Thus the volume of blood is 64-100ths plasma or serum and 36-100ths corpuscles. (See Prof. Stricker's Manual of Histology, Article Blood, by Alexander Rollett, translated by Henry Power, of London, Chap. 13, p. 269.)

VARIATIONS IN SIZE OF THE RED CORPUSCLE.

Prof. Ewell has shown by experiments that many diseases alter the size of the corpuscles, especially microcythaemia, and that they also vary in health.

I have submitted, with his permission, three tables (I, II, and III), showing the result of the measurement of 650 corpuscles of the fresh blood of Prof. Ewell, then being in good health.

These diagrams were first drawn in rectangular co-ordinates.

The horizontal divisions, unless otherwise noted, represent each one division of the eye piece micrometer. The vertical divisions represent the number of corpuscles, each division, unless otherwise noted, representing one corpuscle. The point of origin at the left is for want of space not shown on the diagrams. The curved lines, representing the number of corpuscles, are drawn with the point of origin as their common center, and with radii equaling the number of divisions of the micrometer subtended by them respectively. The curves, therefore, represent on a large scale the relative size of the corpuscles.

Each vertical space one corpuscle, except in case of the last 50, where two spaces=1 corpuscle.
Each horizontal double space 10 divisions of the micrometer.

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