Dr Karl Kruszel­nicki

Australian Geographic - - Contents - with Dr Karl Kruszel­nicki DR KARL is a pro­lific broad­caster, au­thor and Julius Sumner Miller fel­low in the School of Physics at the Univer­sity of Syd­ney. His lat­est book, The Doc­tor, is pub­lished by Pan Macmil­lan. You can fol­low him on Twit­ter: @Doc­torK

Con­cep­tion-con­firm­ing toads

CANE TOADS WERE in­tro­duced into Aus­tralia in 1935 and by the 1950s were a pest in Cairns. In clas­sic Aussie style, Cairns Base Hos­pi­tal’s Louis Tut­tle and Bill Hors­fall found a use for the plen­ti­ful am­phib­ians by de­vel­op­ing a preg­nancy test that used them.

A cou­ple of decades be­fore, in 1928, Ger­man gy­nae­col­o­gists Sel­mar Aschheim and Bern­hard Zon­dek had dis­cov­ered the pres­ence of a dis­tinc­tive hor­mone in the urine of preg­nant women. They in­jected the urine of po­ten­tially preg­nant women into mice, twice a day for three days then killed the mice 100 hours after the first in­jec­tion and ex­am­ined their ovaries. If the sci­en­tists could see new blood ves­sels on the ovaries, they were 99 per cent sure the woman who had sup­plied the blood was preg­nant. This evolved into the Fried­man test for preg­nancy, which in­volved in­ject­ing early morn­ing urine from a woman into an ear vein of a vir­gin fe­male rab­bit, aged at least 12 weeks. The rab­bit was killed after 36 hours so its ovaries could be ex­am­ined: char­ac­ter­is­tic changes in fe­male or­gans showed the woman was preg­nant. One prob­lem with us­ing mice or rab­bits was that they needed to be killed for a di­ag­no­sis. Toads, un­like mam­mals, didn’t.

Tut­tle and Hors­fall’s test in­volved sep­a­rat­ing male and fe­male toads for a few weeks, to en­sure the males were not gen­er­at­ing sperm. At 9.30am, a woman’s urine sam­ple was in­jected into the back of a male cane toad and the an­i­mal was then ex­am­ined at 3pm and 5pm on the same day. If it pro­duced sperm, the preg­nancy test was pos­i­tive. The male toad did not have to be killed and could be used re­peat­edly.

Soon cane toads were be­ing flown out of Cairns air­port to hos­pi­tal lab­o­ra­to­ries across Aus­tralia. The only down­side was that this didn’t re­ally re­duce cane toad num­bers.

In 1960 an im­muno­log­i­cal test for preg­nancy was de­vel­oped. It be­came avail­able over the counter in Canada in 1971 and its use soon spread world­wide.

Cane toad.

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