Conrad utilizes jungle imagery to develop the theme of metaphysical exploration into the heart of humankind. The jungle represents freedom from civilization and its mores and codes; without these artificial rules, man is left to his own devices. Each character is essentially "tested" by his existence in the jungle. Because they do not have to answer to society, the characters in the novel act on what is in their hearts. This theme allows Conrad to reveal the depths of the human soul through a variety of character reactions.
             Early on in Marlow's journey, the jungle represents the unknown; he views it as an enticing and foreign land full of adventure and as something he is longing to experience. As he reveals how he had desired to conquer the unknown and journey to the "blank space[s] on the earth," (348) when he was a boy, he describes his view of the continent of Africa on the map. He says that by the time he had grown up, "[i]t had ceased to be a blank space...it had become a place of darkness" (348) and he goes on to detail his thoughts of the Congo. The "mighty big river," he says "resembl[ed] an immense snake uncoiled, with its head in the sea, its body at rest curving afar over a vast country, and its tail lost in the depths of the land" (348). Through this imagery of the Congo as a snake, Conrad is forewarning the reader of the presence of an impending doom. This imagery is likened to the snake in the biblical story of Adam and Eve, and thus represents temptation and sin. It is a rather ominous sign for Marlow's imminent journey.
             When Marlow gets his appointment as a riverboat captain, he is enthralled with the opportunity of experiencing the unknown. He does not, at this time, comprehend the significance of the journey he is about to commence. His first clue comes when he must visit the Company doctor in Brussels to undergo a physical examination. Aft...