"I can see no other, I must confess." And Scarth raised his eyes just as Dollar's fell from his broad brown brow.
"The other difference is, Mr. Scarth, that the prescription with the strychnine in deadly decigrams has been drawn backward instead of being written forward."
Scarth's stare ended in a smile.
"Do you mind saying all that again, Doctor Dollar?"
"I'll elaborate it. The genuine prescription has been written in the ordinary way—currente calamo. But forgeries are not written in the ordinary way, much less with running pens; the best of them are written backward, or rather they are drawn upside down. Try to copy writing as writing, and your own will automatically creep in and spoil it; draw it upside down and wrong way on, as a mere meaningless scroll, and your own formation of the letters doesn't influence you, because you are not forming letters at all. You are drawing from a copy, Mr. Scarth."
"You mean that I'm deriving valuable information from a handwriting expert," cried Scarth, with another laugh.
"There are no such experts," returned Dollar, a little coldly. "It's all a mere matter of observation, open to everybody with eyes to see. But this happens to be an old forger's trick; try it for yourself, as I have, and you'll be surprised to see how much there is in it."
"I must," said Scarth. "But I can't conceive how you can tell that it has been played in this case."
"No? Look at the start, 'Herr Laverick,' and at the finish, 'Doctor Alt.' You would expect to see plenty of ink in the 'Herr,' wouldn't you? Still plenty in the 'Laverick,' I think, but now less and less until the pen is filled again. In the correct prescription, written at my request to-day, you will find that this is so. In the forgery the progression is precisely the reverse; the t in 'Alt' is full of ink, but you will find less and less till the next dip in the middle of the word 'Mahlzeit' in the line above. The forger, of course, dips oftener than the man with the running pen."
Scarth bent in silence over the lens, his dark face screwed awry. Suddenly he pushed back his chair.