Section 2. That Experiments or Operation of This Nature Shall Be

undertaken only by one of the responsible head-physicians or surgeons of some hospital or public instiution or by his special written authorization; provided only that nothing herein contained shall apply to scientific investigations incapable of causing injury, made by direction of authorities in charge of any institution of learning, upon students, with their consent, for the purpose of testing acuteness of mental action, or for the purpose of investigating other mental or physical phenomena.