[If] he finds it in a stable, he is not responsible for it; in a public domain, he is responsible for it. If it is [in] a graveyard, he may not contaminate himself for it.  If his father says to him: “Contaminate yourself,” or he says to him: “Do not re-turn [it],” he should not obey him.  [If] he unloaded and loaded, unloaded and loaded —- even four or five times —- he is obligated, as it is said (Exodus 23:5): “You shall surely help.” [If] he walked away and sat down, and said: “Since the commandment is [incumbent] upon you, if you want to unload, unload,” he is exempt, as it is said (ibid.): “With him.” If he is old or sick, he is obligated.  It is a commandment in the Torah to unload, but not to load. R’ Shimon says: Even to load. R’ Yose the Galilean says: If it bore more than its [proper] burden, he is not bound to him, for it is said (ibid.): “under its burden” —- a burden which it can bear.