Quote 31
I hesitated long before I put this theory to the test of practice. I knew well that I risked death; for any drug that so potently controlled and shook the very fortress of identity, might, by the least scruple of an overdose or at the least inopportunity in the moment of exhibition, utterly blot out that immaterial tabernacle which I looked to it to change. But the temptation of a discovery so singular and profound at last overcame the suggestions of alarm. (10.3)
Dr. Jekyll well knows the associated risks of using himself as a lab rat (for example, death), but the temptation to dissociate good and evil proves to be too strong.
Quote 32
After all, I reflected, I was like my neighbours; and then I smiled, comparing myself with other men, comparing my active good-will with the lazy cruelty of their neglect. And at the very moment of that vainglorious thought, a qualm came over me, a horrid nausea and the most deadly shuddering. These passed away, and left me faint; and then as in its turn faintness subsided, I began to be aware of a change in the temper of my thoughts, a greater boldness, a contempt of danger, a solution of the bonds of obligation. I looked down; my clothes hung formlessly on my shrunken limbs; the hand that lay on my knee was corded and hairy. I was once more Edward Hyde. A moment before I had been safe of all men's respect, wealthy, beloved—the cloth laying for me in the dining-room at home; and now I was the common quarry of mankind, hunted, houseless, a known murderer, thrall to the gallows. (10.22)
Somehow the transformation from Dr. Jekyll to Mr. Hyde is no longer linked to swallowing a potion, but rather to Dr. Jekyll’s thoughts. We never learn why that shift happens, and it is up to our imaginations to make sense of it.
Quote 33
My provision of the salt, which had never been renewed since the date of the first experiment, began to run low. I sent out for a fresh supply and mixed the draught; the ebullition followed, and the first change of colour, not the second; I drank it and it was without efficiency. You will learn from Poole how I have had London ransacked; it was in vain; and I am now persuaded that my first supply was impure, and that it was that unknown impurity which lent efficacy to the draught. (10.27)
Although Dr. Jekyll is a scientist, he fails to understand fully how his potion works. Perhaps the nature of mankind is beyond the grasp of science.