And we said we can gain active immunity either artificially or either via natural means when infection actually takes place. Now, let's discuss something called passive immunity. Passive immunity basically means we do not develop any memory B cells or memory T cells. And that's because we actually inject antibodies directly into our blood, into our lymph or into our tissue. And by injecting the antibodies we're not exposing the immune system to our antigens and so we're not giving our immune system the adaptive immunity of our immune system the chance to actually develop those antibodies themselves. So another form of immunity is called passive immunity.