Various observers had previously found that the serum of an animal immunized against (a) Lysogenic action.
The serum of an animal thus actively immunized has powerful protective properties towards another animal, the amount necessary for protection being sometimes almost inconceivably small.
Pfeiffer was the first to show that this occurred when the bacterium was injected into the peritoneal cavity of the animal immunized against it, and also when a little of the serum of such an animal was injected with the bacterium into the peritoneum of a fresh, i.e.
Been partially immunized by repeated doses of [that particular] snake-venom.
He immunized 40 persons without mishap and with no more unpleasant results than those occurring after vaccination.