When Otto Loewi collected the fluid from synapses that were involved in slowing a frog's heart, then injected it near the heart of a second frog, he demonstrated that

A) neurotransmitters which are inhibitory can also be excitatory.
B) at least some neurons communicate by releasing chemicals.
C) neurons do NOT communicate by releasing chemicals.
D) communication between a neuron and a muscle is very different than that between two neurons.

By collecting the fluid from synapses involved in slowing a frog's heart and injecting it near the heart of a second frog, Otto Loewi demonstrated that at least some neurons communicate by releasing chemicals, which are now known as neurotransmitters. This was a landmark experiment that provided the first evidence for chemical neurotransmission. Choice A is incorrect because Loewi's experiment did not demonstrate that inhibitory neurotransmitters can also be excitatory. Choice C is incorrect because Loewi's experiment showed that neurons do communicate by releasing chemicals. Choice D is not directly related to Loewi's experiment and is incorrect.