I have your answers. First, a link to a list of other plants
poisonous to your cats:
Poisonous Plants for Dogs and Cats
Q) can someone find out for me exactly how much of the lily leaf do
they need to ingest for it to become indefinitely fatal?
A) It depends on how soon after they chew or eat the plant and you get
to them and realize they need to go to a vet. If kidney damage has
begun, there is no hope of recovery. If you get your cat to a vet
within 6 hours, it MAY survive, but your wallet would be substantially
drained. Tiny amounts can be lethal. The exact "amount" is unknown.
If you came home after an 8 hour work day, and the cat ate the plant
in the morning, it would be too late for a vet to stop the damage and
your cat would die in about 5 days.
...Upon consumption of Easter Lily (the exact amount is unknown), the
cats begin to vomit within an hour or so. The cat then becomes
depressed over the next half day, presumably as the toxin begins to
affect the kidneys. Within 48 to 96 hours after consumption, the cat
will tend to show signs of clinical kidney failure: increased
urination, depression, stomach upset, dehydration. Death tends to
occur within 5 days.
Easter Lily Hazard For Cats
..."All parts of the lily plant are considered toxic to cats and
consuming even small amounts can cause severe poisoning. Cat owners
should be aware of the dangers of lily ingestion and remove them from
their cat's access ..... Within only a few hours of ingestion of the
lily plant material, the cat may vomit, become lethargic, or develop a
lack of appetite. These signs continue and worsen as kidney damage
progresses. Without prompt and proper treatment by a veterinarian, the
cat may develop kidney failure in approximately 36-72 hours..."
This site also lists some Lily varieties known to be poisonous:
Common Name - Scientific Name
Easter Lily - Lilium Longiflorum
Tiger Lily - Lilium Tigrinum
Rubrum Lily - Lilium Speciosum
Japanese Show Lily - Lilium Lancifolium
Day Lily - Hemerocallis Species
Lily family - Toxicity rating: HIGH
Animals affected: The only reported toxicity is in cats.
Dangerous parts of plant: Leaves primarily, stems and flowers may also be toxic.
Lily Poisoning in Cats
You also asked:
Q) do they eat the leaf or do they just chew on it to get the juice
out and that in itself is poisonous?
A) Since even small amounts of ANY part of the plant can lead to fatal
results, ANY Lily ingestion, juice or otherwise, is cause for
immediate concern. Simply chewing on a leaf would be enough exposure.
This listing says it all:
Toxic Plants by Degree of Toxicity
The LILY is on the EXTREMELY TOXIC list.
This link has pictures of some Lily's to keep away from your cats:
Easter Lilies can be deadly for your cat!!!
I hope this helps. I wish the news was better... If you need me to
elaborate on my answer, please ask via the "Request For Clarification"