OPSONINS— TROPINS—BACTERIAL VACCINES 189 
sera— are thermolabile, but those developed during immunization to 
a specific orgamsm—hacteriofwpins—eiTe relatively thermostabile. 
It has been suggested that opsonins or bacteriotropins are not to 
be distinguished from other immune bodies— as normal and specific 
amboceptors or agglutinins. The rapidity with which the opsonic 
index may be increased or diminished within a few hours following 
injections of bacteria, however, would suggest a possible distinction 
between these antibodies and the slowly developing specific bacteri- 
cidal and agglutinating antibodies. 
Vaccine Therapy.— The value of vaccines and of autogenous vac- 
cination in bacterial prophylaxis and bacterial immunization as set 
forth by Wright marks a distinct epoch in bacterial therapeutics in 
spite of the practical failure of his opsonic index determination as 
a theoretical guide to immunization and treatment. He has used 
bacterial vaccines both for prophylaxis— to prevent infection with 
specific bacteria— and therapeutically— to arrest infection. 
Prophylactic Vaccination.— The object of prophylactic vaccination is 
to increase the resistance of the recipient to specific infection. This 
is accomplished by reinforcing the natural initial defenses of the 
body with specific antibodies, generated in the host in response to 
the injection of the specific microorganism as a vaccine. In prophy- 
lactic vaccination the host has ample time to work over the vaccine, 
and by prolonging the treatment through repeated graduated doses 
the maximum degree of immunity may be expected. To attain the 
maximum immunizing effect the bacteria of the vaccine should be as 
near their normal state as possible; that is, they should be endowed 
with all the antigenic properties they possess in the natural disease 
produced by them in the host. 
Following the brilliant work of Jenner with cowpox vaccine and the 
epoch-making observations of Pasteur, observers are fairly agreed 
that the best results from prophylactic vaccination are obtainable 
only by the use of an attenuated living virus. The action of such a 
living virus is, as Theobald Smith^ has aptly expressed it, "a multi- 
titude of feeble blows, each of which produces an immunological 
response." The dangers attending the use of attenuated viruses, 
however, ordinarily preclude their employment, due to inability to 
control the virulence of attenuated cultures. The possibility of 
creating carriers cannot be overlooked. For this reason killed cultures 
are almost invariably selected. 
It is, of course, impossible to utilize an autogenous vaccine in pro- 
phylactic vaccination, but for purposes of immunization a polyvalent 
vaccine is indicated. The action of a dead virus is limited practically 
to a single immimological response, hence the need of repeated inocu- 
lations. 
Preparation of Vaccines.— Much discussion has arisen concerning 
the use of autogenous vaccines as compared with stock or poly\'alent 
1 Jour. Am. Med. Assn., 1913, 60, 1591. 
