“Ah!  I suppose you think I’m safe as far as that goes,” said Frettlby, as they entered the study; “and what did you think of Rolleston’s argument about people being mad?”

“It was amusing,” replied Chinston, taking a seat, Frettlby doing the same.  “That’s all I can say about it, though, mind you, I think there are more mad people at large than the world is aware of.”

“Indeed!”

“Yes; do you remember that horrible story of Dickens’, in the ’Pickwick Papers,’ about the man who was mad, and knew it, yet successfully concealed it for years?  Well, I believe there are many people like that in the world, people whose lives are one long struggle against insanity, and yet who eat, drink, talk, and walk with the rest of their fellow-men, apparently as gay and light-hearted as they are.”

“How extraordinary.”

“Half the murders and suicides are done in temporary fits of insanity,” went on Chinston, “and if a person broods over anything, his incipient madness is sure to break out sooner or later; but, of course, there are cases where a perfectly sane person may commit a murder on the impulse of the moment, but I regard such persons as mad for the time being; but, again, a murder may be planned and executed in the most cold-blooded manner.”

“And in the latter case,” said Frettlby, without looking at the doctor, and playing with a paper knife, “do you regard the murderer as mad?”

“Yes, I do,” answered the doctor, bluntly.  “He is as mad as a person who kills another because he supposes he has been told by God to do so—­only there is method in his madness.  For instance, I believe that hansom cab murder, in which you were mixed up—­”

“I wasn’t mixed up in it,” interrupted Frettlby, pale with anger.

“Beg pardon,” said Chinston, coolly, “a slip of the tongue; I was thinking of Fitzgerald.  Well, I believe that crime to have been premeditated, and that the man who committed it was mad.  He is, no doubt, at large now, walking about and conducting himself as sanely as you or I, yet the germ of insanity is there, and sooner or later he will commit another crime.”

“How do you know it was premeditated?” asked Frettlby, abruptly.

“Any one can see that,” answered the other.  “Whyte was watched on that night, and when Fitzgerald went away the other was ready to take his place, dressed the same.”

“That’s nothing,” retorted Frettlby, looking at his companion sharply.  “There are dozens of men in Melbourne who wear evening dress, light coats, and soft hats—­in fact, I generally wear them myself.”

“Well, that might have been a coincidence,” said the doctor, rather disconcerted; “but the use of chloroform puts the question beyond a doubt; people don’t usually carry chloroform about with them.”

“I suppose not,” answered the other, and then the matter dropped.  Chinston made an examination of Mark Frettlby, and when he had finished, his face was very grave, though he laughed at the millionaire’s fears.