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tions to the Thoma-Zeiss pipette are, the large surface relatively to cubic content, the difficulty of drying the bead quickly enough for use in successive observations, and the presumption that leucocytes will adhere to the bead.

I have always counted both chromocytes and leucocytes in the same film of the diluted blood, and in the same film enumerated the representatives of the various kinds of leucocytes distinguishable, e.g., finely granular, coarsely granular, large hyaline, small hyaline. I imagine the carrying out of the enumeration of all the elements on one and the same film to be a point of importance. The methods of counting in which the enumeration of chromocytes is carried out in one film, that of leucocytes in a second, and the determination of the numerical proportion between varieties of leucocytes in a third and fourth, let a number of possible and probable variants into the observation which are excluded in carrying out the whole operation upon one and the same large film. Certain countings it is naturally impossible to combine in one and the same film; for instance, those dependent on the colour reactions introduced by Ehrlich cannot be combined with enumerations on a living film; but it is possible to translate the one results into the other, and to make in that way the two modes of counting yield, as it were, control observations.

For diluting the blood, I have used the following solution :

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The chromocytes are not laked in it for several hours at the ordinary temperature of the room. The leucocytes of the dog, cat, and rabbit are not killed by immersion in it for several hours; they are reduced to a sluggish condition, and at the ordinary temperature of the room do not locomote over the floor of the counter. This fluid is preferable to Thoma's 0.3 per cent. acetic solution, which soon kills the leucocytes outright, and rapidly destroys much of their finer structural character. The object of the acid solution is to render invisible the chromocytes by laking them. When blood is diluted only ten times, as is usual for counting leucocytes in the Thoma-Zeiss apparatus, the number of chromocytes present tends to obscure the leucocytes. Myself, I met that difficulty in my earlier countings (although chromocytes and leucocytes were always, both of them, enumerated in one and the same film), by rendering the chromocytes, after counting them, invisible by freezing, and proceeding to count the leucocytes. The freezing was done by placing the counter on a carefully levelled freezing microtome, freezing the film for a few seconds, and then letting it thaw again. Most of the chromocytes are thus laked, and the leucocytes are most of them little altered. The difficulty arising from condensation of moisture on the cover glass is met by using the water immersion objective. It seems better, however, to dilute the blood more freely than ten times, and not to freeze the film. I have latterly always used the solution in the proportion of 49 parts to 1 part of blood. This admixture allows of the chromocytes being easily counted, the normal blood of the dog offering then about 33 chromocytes per square on the floor of the counter.

In counting leucocytes one of the most serious mishaps that can occur is for the leucocytes to cluster or "ball." It is obvious that where this has happened the enumeration is useless. The hyaline leucocytes seem less sticky than do the granular leucocytes. There is always, however, a tendency for all leucocytes to clump in this way. In the above fluid in the above proportion, I have had to reject very few observations on account of clumping. The basis obtained for numerical calculation is, of course, reduced by increase of dilution. This

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I have remedied by increasing the area for enumeration on the floor of the counter. I have always counted all the leucocytes found on the whole ruled floorspace of the two counters, i.e., not merely on the squares, but outside them, as far as the ruled lines extended. The area thus obtained was in one of the counters (Counter A) 5 that of the squared area. In the other counter (Counter B) it was 4504, the size of the squared area; this I have treated as 5. As basis for calculation, I have had, therefore, instead of the usually ascertained actual number of leucocytes in 0.01 mm. of blood, the actual number in 00215 mm. of blood, a basis more than twice as wide. The counting has been made on the Zeiss movable stege on his Stativ IV, 1, with the dry 4 mm. apochromatic objective, usually combined with ocular 8. Countings have been occasionally carried on on the warm stage (Israel's).

The amount of hæmoglobin in the blood I measure by the Gower's instrument, by the light of a Welsbach lamp reflected from a vertical sheet of white paper not otherwise illuminated.

The specific gravity of the blood is estimated by Roy's method, as in the observations by Copeman and myself. The specific gravity of the blood serum is also observed by Roy's method. The blood is previously centrifuged in capillary tubes. Havilland and Lloyd Jonest have both employed the centrifuge for separating corpuscles from fluid in minute quantities of blood received into capillary tubes.

The exact procedure with me has been as follows. A drop of blood, as it exudes from a prick in the skin, is taken by capillarity into a fine, freshly drawn glass tube, like a vaccine tube, but longer, and bent into a U shape. The capillary U-tube is then placed with its bent end downwards into a "bucket" on the centrifuge, or in a radial slot on a vulcanite disc; the two open ends will then lie toward the centre of rotation, and in a few minutes a clear layer of serum or plasma is obtained in each limb of the tube. The specific gravity of the supernatant fluid can be readily ascertained by Roy's method. I say serum or plasma, because it is surprising how often no trace of fibrin seems to exist in the clear layer, even on standing for a long time.

The clear fluid I have often found to be absolutely cell free. I shall refer to the fluid as serum, but I suspect that in several instances it was pure plasma.

Where the temperature is recorded, the rectal temperature in degrees centigrade is meant. By respiratory rate is meant number of inspirations per minute.

II.

The varieties of hæmic leucocytes which I have attempted to distinguish are explained more fully on pp. 186–194. The nomenclature adopted is based on Wharton Jones§ and Max Schultze.||

* Journal of Physiology,' vol. 5, p. 9, 1884.

Journal of Physiology,' vol. 9, p. 8, 1890.

'British Medical Journal,' September 23, 1893.

§ "The Blood Corpuscle considered in its different Phases of Development," 'Phil. Trans.,' 1846, p. 64.

|| Archiv für Mikroskopische Anatomie,' vol. 1, p. 1, 1863.

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Differences between Cat's Blood and Dog's Blood.

The number of chromocytes per unit volume blood is greater in cat's blood than in dog's blood. The individual chromocytes are smaller in the former; according to Gulliver, the average diameter in cat is 1/4404 in.; in dog, 1/3542 in. The ratio of leucocytes to chromocytes in normal cat's blood is distinctly lower than in dog's blood; this is probably a result of the greater number of the smaller chromocytes per unit volume of cat's blood.

In the blood of nearly one half of the dogs I have examined, a few nucleated chromocytes have been met with. It has been so in some instances with old dogs (in half-grown puppies they are found in numbers); in all instances the dogs were not known to be ailing; some were certainly very active and well-nourished. The nucleated chromocytes were always of the kind called normoblasts. In adult cats the blood seems to contain nucleated chromocytes less commonly, but I have met with them.

The specific gravity of the serum of cat's blood has in my experiments averaged distinctly higher than that of dog's blood.

The coarsely granular leucocyte appears rather more numerous in cat's blood than in dog's. Certain differences between the coarsely granular leucocytes in the two species will be mentioned in a short description of the leucocytes (p. 189.)

(1.) The Seat of Acute Local Inflammation is in the Limb.

The inflammation was induced in the extremity of the limb in the way above described.

The results on the blood will be best shown by quoting some examples.

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* 'Proceedings of the Zoological Society of London,' June 15, 1875.

VCL. LV.

N

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coarsely granular leucocytes to total leucocytes..

11-11.15 A.M. Temperature, 38.8°. Respiration, 20. Lesion established in both hind legs.

12.40 P.M. Temperature, 38°. Respiration, 18.

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leucocytes per mm. blood.

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hyaline leucocytes per mm. blood (the small kind very
scarce).....

coarsely granular leucocytes per mm. blood...
irregularly nucleate leucocytes per mm. blood

Ratio of leucocytes to chromocytes......

hyaline leucocytes to chromocytes.....
coarsely granular leucocytes to chromocytes.

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coarsely granular leucocytes to total leucocytes....

3.15 P.M. Temperature, 38°. Respiration, 16.

Sp. gr. of blood from ear.

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leucocytes per mm. blood

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hyaline leucocytes per mm. blood (small kind less

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coarsely granular leucocytes per mm. blood.
irregularly nucleate leucocytes per mm. blood

Ratio of leucocytes to chromocytes......

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coarsely granular leucocytes to total leucocytes.....

5.15 P.M. Temperature, 38°. Respiration, 14.

Sp. gr. of blood from ear.....

Hæmoglobin value..

......

Sp. gr. of blood serum.

Number of chromocytes per mm. blood..

leucocytes per mm. blood...

15,304

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coarsely granular leucocytes per mm. blood
irregularly nucleate leucocytes per mm. blood

Ratio of leucocytes to chromocytes....

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10,200,000

32,956

890

none found.*

32,100

1: 309

1 : 11,460

1:37

"None found" refers, unless otherwise stated, to search in the two counters.

12 noon next day. Temperature, 37.8°. Respiration, 22.

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coarsely granular leucocytes per mm, blood...
irregularly nucleate leucocytes per mm. blood..

Ratio of leucocytes to chromocytes....

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hyaline leucocytes to chromocytes.....

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The smaller kind of hyaline leucocyte forms about 15 per cent. of all the hyaline leucocytes.

12 noon next day. Temperature, 34°. Respiration, 24.

Sp. gr. of blood from ear..

Hæmoglobin value...

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1,430.

none found. 28,110

1: 290

1: 6,153

1:20:5

1.078
91
1.024
8,300,000

12,630

1,280

none found.

11,070

1: 657
1 : 6,484

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1.066
69

1.0245

8,126,600

7,500

1,100

irregularly nucleate leucocytes per mm. blood

Ratio of leucocytes to chromocytes.....

417

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coarsely granular leucocytes to total leucocytes..

10.30-10.45 A.M. Lesion established in one limb only.

11.15 A.M. Temperature, 38.6°. Respiration, 20. Sp. gr. of blood taken from ear

Hæmoglobin value..........

Sp. gr. of blood serum..

...

Number of chromocytes in mm. blood

1:18

1.072

78

1.025 8,910,000

6,670

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leucocytes in mm. blood

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