until the early 20th century, scientists assumed that the majority of synaptic communication in the brain was electrical. however, through the careful histological examinations by ramón y cajal (1852–1934), a 20 to 40 nm gap between neurons, known today as the synaptic cleft, was discovered. the presence of the gap suggested chemical messengers moved across the synaptic cleft. in 1921 german pharmacologist otto loewi (1873–1961) confirmed that neurons can communicate by releasing chemicals. by experiments involving the vagus nerves of frogs, loewi was able to slow the heart rate of frogs by controlling the amount of saline solution present around the vagus nerve.