At length he began his little lecture, for all the world as though this were one of his classes at the University, as though there were at stake some matter of chemical reaction.

“I need not tell you, ladies and gentlemen, that this is a highly scientific age in which we live.”  His tones were leisurely, businesslike, cool.  “Your own profession, the moving picture, with all its detail of photography and electricity, its blending of art and drama and mechanics, is indicative of that, but”—­a pause for emphasis—­“it is of my own profession I wish to talk just now, the detection and prevention of crime.

“Criminals as a whole were probably the very first class of society to realize the full benefit of modern science.  Banks and business institutions, the various detective and police forces, all grades and walks of life have been put to it to keep abreast of the development of scientific crime.  So true has this been that it is a matter of common belief with many people that the hand of the law may be defied with impunity, that justice may be cheated with absolute certainty, just so long as a guilty man or woman is sufficiently clever and sufficiently careful.

“Fortunately, the real truth is quite the reverse.  Science has extended itself in many dimensions of space.  With the use of a microscope, for instance, a whole new world is opened up to the trained detective.

“Everyone knows now that the examination of hands and fingers is an infallible aid in the identification of criminals and in the proof of the presence of a suspect at the scene of a crime—­I refer to fingerprints, of course.  But fingerprints are only one small detail in this department of investigation.  Our criminals know that gloves must be worn, or any smooth surface wiped so as to remove the prints.  In that way they believe they cheat the microscope or the pocket lens.

“As a matter of fact few people have thought of another way of gaining evidence from the finger tips, but it is a method possible to the scientist, and is not only practicable but exceedingly effective.  In time it will be recognized by all specialists in crime.  Now I refer to the deposits under the finger nail.

“Indeed, it is surprising how many things find their way under the nail and into the corners of the cuticle.”  Kennedy indicated the files and pocket knives visible in the shaded square of light before him.  “The value of examining finger-nail deposits becomes evident when we realize that everyone carries away in that fashion a sample of every bit of material he handles.  To touch a piece of cloth, even lightly, will result in the catching of a few of its fibers.  Similarly, the finger nails will deposit either a small or large portion of their accumulation upon such things as the knife blades or files used to clean them; and there identification still is possible.  Nothing in the world is too infinitesimal for use as evidence beneath the microscope.