While he protests that he knows nothing of how the stone has disappeared, he stubbornly refuses to allow them to search his clothes.  The effect upon the other guests may easily be imagined.  Later, however, one of the guests having followed him home, it is discovered that the poor old man has merely filled his pockets with different delicacies from the table, and has taken them home to his sick grandchild.  Subsequently it is discovered that the Hindoo servant has taken the jewel, and he is arrested and punished.  In the moment that the attention of the guests was directed elsewhere, after the old gentleman had laid it on the table, the servant had snatched up the jewel and dropped it into a half-filled water glass, where it remained undiscovered while the servant was searched with the others.  It is pretty generally known that an unset pure diamond, if dropped into a glass of water, becomes invisible.

Some time during 1911, one of the producing companies released a picture entitled “The Class Reunion.”  To get the plot of the photoplay story, simply substitute an impecunious professor for the old gentleman in the short-story.  Instead of the Hindoo servant, have one of the pupils—­if our memory serves—­turn out to be the thief, and have him drop the jewel—­which is a ruby, and not a diamond—­into a glass of red wine instead of into a glass of water.  In all other particulars the two stories were identical.

Only a few months later, this plot cropped up again—­in fiction form—­in a prominent American magazine.  Then, in the release of another well-known company, of January 13, 1913, it again did service in the photoplay “The Thirteenth Man,” where the inevitable banquet is the annual reunion of “The Thirteen Club.”  The theme has now become so hackneyed that, as the list given in Chapter XVI shows, it is no longer serviceable for photoplay purposes.

Obviously, these facts are cited not to discredit the companies referred to, but solely to emphasize the difference between the genuinely new twist as exemplified in Conan Doyle’s “The New Catacomb,” and the dangerously close similarity as exhibited in at least one of the two photoplays just referred to as following the plot of the Strand story.

It must not be inferred, however, that all cases in which the themes of short-stories are developed into photoplays with very little change are plagiarisms, either conscious or unconscious.  Many important companies are negotiating constantly with the magazines for the right to photodramatize their most suitable short-stories.  Sometimes this is done with the consent of the author and the plot of the story used substantially without change, while in other instances the plot is freely changed, only the germ being used.  It is particularly in such cases that we must be careful not to charge plagiarism.