A
complement-fixing
antigen specific for
scrub typhus occurs in the body fluids and tissues of infected mice, white rats, and cotton rats. The specific serological substance is demonstrable only in those animals which develop a rapidly fatal disease after an incubation period of a few days. Such an experimental
infection is induced in mice and rats by the
intravenous injection of
suspensions of yolk sac rich in R. orientalis.
Ether extraction is an important step in the preparation of a
complement-fixing
antigen from tissues of mice dying with
scrub typhus. The Imphal No. 8 and Calcutta strains of R. orientalis are indistinguishable on the basis of
complement fixation and cross-immunity tests. The
complement-fixing
antigen in body fluids of infected mice and rats and in our preparations of tissues from such animals occurs as a soluble
antigen. Under the proper conditions the soluble
antigen can be stored or dehydrated without loss of serological activity.