What was Loewi’s evidence that neurotransmission depends on the release of chemicals?

a. He applied adrenaline to muscles and saw them contract.

b. He applied drugs at various synapses and observed excitatory and inhibitory postsynaptic potentials.

c. He stimulated one frog’s heart, collected fluid around it, transferred it to another frog’s heart, and saw change in its heart rate.

d. He stimulated certain nerves, collected the fluid around their terminals, and analyzed the contents chemically.