270 BACTERIOLOGICAL EXAMINATION OF MATERIAL 
introduced parenterally into the tissues direct. The site of inocula- 
tion is usually the skin, the body fluids or body cavities. It must be 
remembered that infection through unnatural channels does not 
necessarily reproduce a replica of the original infection. The skin 
must necessarily be entered to reach the deeper tissues. For this 
reason the site of injection should be shaved and sterilized with tincture 
of iodine.^ 
Cutaneous Inoculation. — (a) Cutaneous: Material is rubbed upon 
a shaved area of skin. 
(6) Intracutaneous: Injection is made directly into the skin. 
((?) Subcutaneous: Material is introduced beneath the skin. A 
pocket is sometimes made by separating the skin from the cellular 
subcutaneous tissue, into which solid fragments of tissue are placed. 
The skin over the abdomen is a common site for inoculation with 
fluid cultures; the hypodermic needle is introduced at one side of 
the median line and forced through the subcutaneous tissue in a 
transverse direction, to a point well beyond the median line on the 
opposite side. The abdominal wall becomes somewhat tense and 
does not permit leakage to the outside if this procedure is followed. 
Intravenous inoculations are made into the blood stream either 
through a vein, or directly into the heart. Rabbits are readily injected 
through the marginal ear veins; the vein is pinched close to the head 
of the animal and gently massaged; this causes distention and makes 
the vein prominent. A hypodermic needle will then readily enter 
the vein; it should be gently forced along its course for a centimeter 
or two before injection. 
Body Cavities. —The peritoneal cavity is commonly selected, but 
intrapleural injections are readily made. Before introducing a hypo- 
dermic needle into the peritoneal cavity, the animal, guinea-pig or 
rabbit, is held head downward to permit the intestines to pass ante- 
riorly as far as possible. The needle is first introduced somewhat 
obliquely through the abdominal skin posteriorly, then directly into 
a fold of the abdominal wall pinched between the fingers. The needle 
should be pressed in imtil resistance to its passage has ceased. .Unless 
the precaution is taken to dip the point of the needle in sterile vase- 
line, some of the contents will be introduced into the cutaneous or 
subcutaneous tissues as well as the peritoneal cavity. The "Kitchens" 
syringe with its side-arm containing salt solution to rinse the entire 
charge from the needle before withdrawal from the animal is highly 
recommended for this purpose. 
Intracerebral injections are made either through the optic foramen, 
or through the dura after trephining the skull. 
Intratracheal injections are occasionally made, but more commonly 
the material is introduced deep into the bronchi through a flexible 
rubber camuda. The animal should be anesthetized for this operation. 
^ Tincture of iodine should be freshlj'' prepared and painted upon the drj- surface it 
is desired to sterilize. Sterilization is usually arcom])lishcd after two or three minutes' 
exposure to the iodine solution. 
