143 Essays on Infinite Lifespans   Brian Wowk Cryobiologists, professional scientists who study the effect of cold on living things, decided long ago that they did not want their field associated with cryonics. [36] The Society for Cryobiology bylaws even provide for the expulsion of mem- bers  that  practice  or  promote  “freezing  deceased  persons”. The  result  has  been  the  polarization  of  cryobiologists  into either  outspoken  contempt  or  silence  concerning  cryonics. The contempt camp typically speaks of cryonics as if it has not changed in 40 years. This political environment, plus the fact  that  most  cryobiologists  work  outside  the  specialty  of organ cryopreservation, makes obtaining informed cryobio- logical information about cryonics very difficult. The most important cryobiological fact of cryonics (other than its current irreversibility) is that cryoprotectant chemi- cals can be successfully circulated through most of the major organs of the body if blood clots are not present. We can conclude  this  by  simply  considering  that  everything  now known about long-term preservation of individual organs was learned by removing and treating those organs under condi- tions similar to ideal cryonics cases. It is generally observed that the quality of cell structure preservation (as revealed by light and electron microscopy) is very poor when there is no cryoprotectant, but steadily improves as the concentration of cryoprotectant is increased (provided toxicity thresholds are not exceeded). Recent years have seen a trend toward using higher  cryoprotectant  concentrations  in  cryonics,  yielding structural preservation that is impressively similar to unfrozen tissue. [35] Extraordinary claims require extraordinary evidence. While it is plausible that mechanical CPR and rapid cooling can keep the brain alive long after cardiac arrest, cryonicists need to pro- vide more oxygenation and blood chemistry data from more cases to support this claim. While it is plausible that morpho- logical vitrification of major organs can now be achieved with