"to the sellers of invigorating electric belts and to the inventors of patent medicines"

Quack doctors. Conrad clearly had a very dim view of the people who peddled dubious wonder cures such as electrohomeopathy as he uses them for negative comparisons several times in the narrative. Between 1880 and 1930 there were two electric remedy devices on the market, both of which claimed to combat fatigue and aging by administering electric shocks and vibration to various parts of the body.