In order to overcome the limitations and problems that earlier apparatus and methods for determining physiological effects of heat flux with a cryogenic substance applied to an organism have experienced, it is proposed that the apparatus (10) comprises:- a heat flux sensor (12);- a cryogen delivery apparatus (16) spaced apart a distance (D1) from the heat flux sensor (12); and- at least one organism culture (28) supported on the heat flux sensor (12) in a path of delivery of the cryogenic substance from the cryogen delivery apparatus (16) to contact the at least one organism culture (28).The corresponding method for determining physiological effects of heat flux with a cryogenic substance applied to an organism comprises:- testing at least one organism culture (28) for heat flux with a cryogenic substance; and- establishing an amount of heat transfer required at the organism for achieving maximum destruction of said organism.