OPSONINS-TROPINS— BACTERIAL VACCINES 191 
transfer to the counting chamber. An enumeration of the bacteria is 
made in precisely the same manner that a blood count is made. 
8. Dilute the suspension to the required degree with phenol solution, 
so that the finished vaccine shall contain 0.25 to 0.5 per cent of it. 
This is the finished vaccine. 
9. Redetermine sterility if necessary. 
Sensitized Vaccines.— Killed bacteria which have been immersed 
in a specific serum — sensitized vaccines— are said to be less liable 
to produce general and local reactions. The immunity developed 
in response to the injection of these sensitized vaccines is said to 
appear more rapidly, and doses thirtyfold those of unsensitized vaccines 
may be injected without serious effect. 
Lipomccines.—\\hitmore, Fennel and Petersen^ have prepared 
vaccines suspended in sterile neutral oils; lanolin has been used to 
emulsify the bacterial bodies before the final dilution is made with the 
oil. The process consists essentially in removing bacterial growths 
from the surface of large Petri dishes. Culture; place the bacterial 
substance in a vacuum apparatus and cool rapidly to a xery low tem- 
perature. xA.fter drying, the dry, flaky mass is ground in sterile ball 
mills for ten hours; first alone, then wath lanolin, to the extent of 10 per 
cent of the final dilution desired. Dilution is practised, using sterile 
olive oil or similar neutral oil, preferably of the vegetable series. 
Lewis and Dodge- have found that the finally diluted vaccine, con- 
taining 2 mg. of dry bacterial substance per cubic centimeter, may be 
sterilized at 130° C. for three hours, or at 120° C. for twelve hours, 
without injuring the antigenic properties of the pneumococcus; the 
typhoid bacillus is somewhat injured by this process. 
The use of lipovaccines makes it possible to induce a practical 
increase in immunity with a single injection. Suspensions of typhoid, 
paratyphoid alpha and paratyphoid beta bacilli, containing about 2.5 
billion of each made up as a single lipovaccine has great military 
advantage over the older vaccines. Lipovaccines for meningococci, 
dysentery bacilli, typhoid and paratyphoid bacilli and cholera vibrios 
have been prepared. 
The Injection.— The skin at the site of injection is cleaned with 
soap and water and then with alcohol; or better, after carefully dry- 
ing it is painted with tincture of iodine. The required amount of 
vaccine is injected subcutaneously through this area, from a sterile 
syringe. In typhoid, vaccines have been injected directly into a vein. 
This is at present not usually recommended, and there have been some 
unfortunate results following this method of administration. 
The Dosage and Frequency of Injection.— It is advisable to begin 
with small doses of vaccine, quantities which past experience has 
shown to do no harm so far as can be determined by clinical evi- 
dence, and to increase the size of the dose gradually, the injections 
1 Jour. Am. Med. Assn., 1918, 70, 427, 902. 
2 Jour. Exper. Med., 1920, 31, 169. 
