They would be constantly together.
They would either prove or disprove my theory that men and women were but machines of passion.

I knew that they would stay at this place during the three months I had allotted for my experiment, for I paid them a high price.

The girl, when she found no American family, was told to wait until they arrived.

The man, of course, had plenty of supposed work to keep him there." "I understand," repeated Philip.
"The second couple," continued the doctor, forcing himself into a chair opposite Philip, "were in a similar way sent up here--to an obscure northern post which I have reason for not naming.

And the third couple went to a feverish district down in Central America." He rose from his chair again, and Philip was silent while the doctor went to his great-coat and from somewhere within its depths brought out fresh cigarettes.