The toxin  may or may not be present in strains of  er  C diphtheria  and this is  just an immunological test so I wo won't explain it in detail but what you can see is a  a strip of er, filter paper which has been bathed in anti-toxin and  growth of various different strains of the organism  erm  which, some of which do produce the toxin  you can see lines of precipitation here  and some of which don't produce the toxin.