As the surgeon's chain saw chiseled through bone above a knee, the observers gasped. Some clamped their hands over their eyes. Others turned their heads, cringing. But roughly a dozen sets of eyes were riveted to the screen where video of the surgery was unfolding, watching until the surgeon finished stitching up the site of the amputation.

Huddled in a darkened classroom at Cherry Hill High School West on Thursday, 49 students watched -- or turned away at times -- as surgeons from Deborah Heart and Lung Hospital performed two amputations. One patient lost a leg, another the toes of one foot.

The live, hour-long interactive forum was intended to help the students decide whether they wanted to pursue careers in medicine. Dr. Matthew Samra of Deborah added live narration to the prerecorded surgeries, which were streamed to student audiences at Cherry Hill West and 12 other high schools in Camden and Burlington Counties. On laptops, students keyed in questions to Samra throughout the presentation.

The teaching hospital in Browns Mills, Burlington County, is in its fifth year of streaming the videos.

"Anyone can look up a surgery on YouTube, but the opportunity for a doctor to actually tell you what's happening in real time and answer questions is something that not a lot of people have, much less in high school," said Nicole Schmalbach, an 18-year-old senior at Cherry Hill West.

This was the second year Schmalbach, an aspiring neurosurgeon, had watched the Deborah live stream through her science courses. She said the presentation made her want to be a surgeon even more. She messaged Samra, as he described the surgeries by his colleagues, to ask if the toe amputation patient would later have difficulties with balance. The answer was no.

Samra, a cardiothoracic and vascular surgeon with the Browns Mills hospital, said afterward  that he was impressed by his student audience. The students were thinking at an advanced level for their age, he said. Schmalbach's question, he said, indicated that she would make a great doctor. Doctors are always supposed to think about the ramifications of surgeries they perform, he said.

The man in his 50s who underwent toe amputation was a smoker for more than 25 years and a diabetic. An infection had spread in his toes, Samra said.

The knee amputee also was a smoker who previously had the leg amputated below the knee. That surgery was unsuccessful, leading to the above-the-knee amputation, which was necessary for proper healing, he said.

At Cherry Hill West, only anatomy, physiology, and biology II students were invited to attend the surgical forum, said Sandra Castellani, who teaches those subjects. While most of those students are looking to pursue careers in health professions, she said, some were just interested in applying the scientific knowledge to other potential pursuits.

Senior Natalie Jester, 17, said that she wants to eventually own a dance studio and that understanding anatomy is helpful to a dancer's success.

Castellani hoped her students gained a better appreciation of physiology Thursday. For those with ambitions of becoming physicians, she said, the event provided a foretaste of that  profession.

"When you're in college, you often have to pay for these kinds of things," she said.