h out the last traces of the
inoculum.

8. Withdraw the catheter.

9. Label, etc.

_B. Rats and Mice (Mark's Method)._

1. Secure the animal in the vertical position.

(a) _Rat._--Take a pair of catch sinus forceps about 22 cm. in length
and seize the animal by the loose skin of the head as far forward as
possible--fix the forceps, and holding the instrument vertically upward,
transfer to the left hand of an assistant who secures the animal's tail
between the fingers grasping the handle of the forceps. (See Fig. 191.)

[Illustration: FIG. 191.--Intragastric inoculation of rat.]

(b) _Mouse._--An assistant grasps the loose skin between the ears as far
forwards as possible between the forefinger and thumb of the left hand.
He now grasps the tail with the right hand, draws the mouse straight and
passes the tail between the fourth and little fingers of the left hand
and secures it there.

2. The assistant takes a closed pair of thin-bladed forceps in his right
hand, passes the ends into the animal's mouth, then allows the blades to
separate. This opens the animal's jaw and serves as a gag.

3. Moisten the sterilised oesophageal tube with sterile water. (This
tube is of silk rubber, 6.5 cm. in length, with the distal end rounded,
the proximal end mounted in a syringe needle head, which fits the
nozzles of the two sterile syringes to be used.)

4. Grasp the tube about its middle and pass it into the animal's mouth,
downwards and a little to one side or the other until its length is lost
in the digestive tract and mouth. Gentle guidance is alone necessary. Do
not use any force.

5. Take up the required dose of inoculum into the syringe; insert the
nozzle of the syringe into the needle-mount, and force the piston down.

6. Steadying the needle-mount with the left hand, detach the syringe.

7. Draw up some sterile water in the second (sterile) syringe, and
inserting its nozzle into the needle-mount force a few drops of water
through the tube to wash it out.

8. With one quick upward movement remove the tube from the animal's
mouth.

9. Label, etc.

One other method of inoculation remains to be described, which does not
require operative interference.

~11. Feeding.~--

1. _Fluid Inoculum._--Small pieces of sterilised bread or sop
(sterilised in the steamer at 100 deg. C.) are soaked in the fluid
inoculum and offered to the animals in a sterile Petri dish or capsule.

2. _Solid Inoculum._--Small pieces of