Pacific hagfish (Eptatretus stoutii) produce copious amount of viscous slime when physically threatened or agitated. The slime is composed of threads (produced by gland thread cells) and glycoproteins (produced by gland mucous cells) which interact to form an integrated gel network that acts as a defence against gill-breathing predators. This thesis investigates the mechanisms that drive vesicle swelling and slime formation. I tested two hypotheses, the Hofmeister hypothesis and the cationic gel hypothesis. The Hofmeister hypothesis predicts that swelling depends on the Hofmeister properties of the solutes in solution; “kosmotropes” stabilize proteins while “chaotropes” solubilize proteins and should cause swelling. My findings were not consistent with these predictions; my results show that swelling occurs even in the presence of strong kosmotropes. I also found that solutions containing multi-charged anions stabilized the glycoproteins and monovalent anions induced rapid swelling. The cationic gel hypothesis states that the glycoproteins are positively charged and are stabilized in vivo by multivalent anions. This hypothesis predicts that altering the ionization state of ions in solution should alter the swelling response. Indeed, this is what I found. Overall, these results are consistent with the idea that the glycoproteins are positively charged although this hypothesis needs to be tested more thoroughly before it can be accepted.