These comments suggest what about Marlows upcoming experience?

These comments suggest that Marlowe is merely a part of an experiment.

"The old doctor felt my pulse, evidently thinking of something else the while. 'Good, good for there,' he mumbled, and then with a certain eagerness asked me whether I would let him measure my head. Rather surprised, I said Yes, when he produced a thing like calipers and got the dimensions back and front and every way, taking notes carefully. He was an unshaven little man in a threadbare coat like a gaberdine, with his feet in slippers, and I thought him a harmless fool. 'I always ask leave, in the interests of science, to measure the crania of those going out there,' he said. 'And when they come back, too?' I asked. 'Oh, I never see them,' he remarked; 'and, moreover, the changes take place inside, you know.' He smiled, as if at some quiet joke. 'So you are going out there. Famous. Interesting, too.' He gave me a searching glance, and made another note. 'Ever any madness in your family?' he asked, in a matter-of-fact tone. I felt very annoyed. 'Is that question in the interests of science, too?' 'It would be,' he said, without taking notice of my irritation, 'interesting for science to watch the mental changes of individuals, on the spot, but...'