oculated animal of the same species, and which is termed "normal"
serum. In view of minor differences in constitution exhibited by the
serum of various individuals of the same series, it is usual to employ a
mixture of sera obtained from several different normal animals of the
same species as the inoculated animal, under the term "pooled serum."
The method of collecting blood (e. g., from the rabbit) for
serological tests is as follows:

~Collection of Serum.~

_Apparatus required:_

Razor.
Liquid soap.
Cotton-wool.
Lysol 2 per cent. solution, in drop bottle.
Ether in drop bottle.
Flat Hagedorn needles.
Blood pipettes (Fig. 16, page 12).
Centrifugal machine.
Centrifuge tubes.
Glass cutting knife.
Bunsen flame.
Writing diamond or grease pencil.

METHOD.

1. Shave the dorsal surface of the ear over the course of the posterior
auricular vein (see Fig. 192).

2. Sterilise the skin by washing with lysol.

The lysol should be applied with sterile cotton-wool and the ear
vigourously rubbed, not only to remove superficial scales of epithelium,
but also to render the ear hyperaemic and the vein prominent.

3. Remove the lysol with ether dropped from a drop bottle, and allow the
ether to evaporate.

4. Puncture the vein with a sterile Hagedorn needle.

5. Take a small blood-collecting pipette (Fig. 161) and hold it at an
angle to the ear, one end touching the issuing drop of blood, the other
depressed.

The blood will now enter the pipette at first by capillarity; afterward
gravity will also come into play and the pipette can be two-thirds
filled without difficulty.

6. Hold the tube by the end containing the blood, the clean end pointing
obliquely upward--warm this end at the bunsen flame to expel some of the
contained air; then seal the clean point in the flame.

[Illustration: FIG. 192.--Collecting blood from rabbit.]

7. Place the pipette down on a cool surface (e. g., a glass slide).
The rapid cooling of the air in the clean end of the pipette creates a
negative pressure, and the blood is sucked back into the pipette,
leaving the soiled end free from blood. Seal this end in the bunsen
flame.

8. Mark the distinctive title of the specimen (e. g., animal's number)
upon the pipette with a writing diamond or grease pencil.

9. When the sealed ends are cold and the blood has clotted, place the
pipette on the centrifuge, clean end downward; counterpoise an