Mushroom ET MIX CASING bulk substrate?

Can an ET Mix casing soil be used as a bulk substrate in growing mushrooms? If there is a difference between bulk substrate and casing can anyone tell me the difference?

from what I have read/watched (numerous) I believe it is to confuse us!
casing should be what you start with to get the Mycelium to "run"
then transferred to a "substrate" IT REALLY Iz ENOUGH 2 confuse the crap outta of us! but I have done extensive research and this is my only conclusion -which I could be wrong-so if ANYONE out there would like to correct me~
Please do so, thanks and PeAcE only~

I believe that you want your substrate to be nutrient rich so that the myc grows well through it. The casing layer inturn should be nutrient deprived as a trigger for the myc to begin fruiting. So it would be my belief that a casing soil would make a very poor bulk substrate. Javadog, or canndo would be the guys to give the best answer I think.

spawn is what you use to innoculate bulk substrate. It can be any particles that are fully engulfed in mycelium. Thunder at has the rest correct.

Hehe I knew I just had to call your name .