“What's this thing here?” he demanded.

“A water-pump,” Markfield answered, as though not quite following the Inspector's train of thought.

“And this rubber tubing, what sort of stuff is it?”

“Pressure-tubing. What about it?”

“Does Dr. Silverdale use anything of that sort?”

“Everybody in the place uses it. Whenever one wants quick filtering one uses a water-pump with pressure-tubing connections.”

“Miss Deepcar and Miss Hailsham use it, then?”

“I should think there are a dozen or two of these pumps in this department alone. They're ordinary fittings in every chemical laboratory. If I may ask, Inspector, what are you getting at?”

Flamborough switched off to a fresh line without making any direct reply.

“Is Miss Deepcar here to-day?”