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Suffering occurs when the pain leads the person to feel out of control , when the pain is overwhelming , when the source of the pain is unknown , when the meaning of the pain is perceived to be dire , and when the pain is chronic ( Cassell , 1982 ) . However , P. persimilis should not be released where F. acarisuga is becoming established because they are known to eat midge eggs if prey is limited ( Gillespie 1998 ) . It is in the combined effect upon cardiac action that toxic interactions of THC and stimulants could be dangerous , but there are no clear indications in the literature for humans , and the evidence from animal studies is mixed ( Siemens , 1980 ) . The newest AD medication is memantine ( Namenda ) , which is prescribed to treat moderate to severe AD symptoms ( Reisberg et al ., 2003 ; Tariot et al ., 2004 ) . Nevertheless , the transect survey contacted more groups that were seen only once during the total survey , and also located more solitary animals than the census walks combined ( Table 2 ) , although a few of the latter were determined by a census walk to be in groups after all .