He stopped the film.  The next picture was a sort of enlarged and elongated house fly, apparently, of sombre grey color, with a narrow body, thick proboscis and wings that overlapped like the blades of a pair of shears.  “This,” he went on, “is a picture of the now well known tse-tse fly found over a large area of Africa.  It has a bite something like a horse-fly and is a perfect blood-sucker.  Vast territories of thickly populated, fertile country near the shores of lakes and rivers are now depopulated as a result of the death-dealing bite of these flies, more deadly than the blood-sucking, vampirish ghosts with which, in the middle ages, people supposed night air to be inhabited.  For this fly carries with it germs which it leaves in the blood of its victims, which I shall show next.”

A new film started.

“Here is a picture of some blood so infected.  Notice that worm-like sheath of undulating membrane terminating in a slender whip-like process by which it moves about.  That thing wriggling about like a minute electric eel, always in motion, is known as the trypanosome.

“Isn’t this a marvellous picture?  To see the micro-organism move, evolve and revolve in the midst of normal cells, uncoil and undulate in the fluids which they inhabit, to see them play hide and seek with the blood corpuscles and clumps of fibrin, turn, twist, and rotate as if in a cage, to see these deadly little trypanosomes moving back and forth in every direction displaying their delicate undulating membranes and shoving aside the blood cells that are in their way while by their side the leucocytes, or white corpuscles, lazily extend or retract their pseudopods of protoplasm.  To see all this as it is shown before us here is to realise that we are in the presence of an unknown world, a world infinitesimally small, but as real and as complex as that about us.  With the cinematograph and the ultra-microscope we can see what no other forms of photography can reproduce.

“I have secured these pictures so that I can better mass up the evidence against a certain person in this room.  For in the blood of one of you is now going on the fight which you have here seen portrayed by the picture machine.  Notice how the blood corpuscles in this infected blood have lost their smooth, glossy appearance, become granular and incapable of nourishing the tissues.  The trypanosomes are fighting with the normal blood cells.  Here we have the lowest group of animal life, the protozoa, at work killing the highest, man.”

Kennedy needed nothing more than the breathless stillness to convince him of the effectiveness of his method of presenting his case.

“Now,” he resumed, “let us leave this blood-sucking, vampirish tse-tse fly for the moment.  I have another revelation to make.”

He laid down on the table under the lights, which now flashed up again, the little hollow silver cylinder,

“This little instrument,” Kennedy explained, “which I have here is known as a canula, a little canal, for leading off blood from the veins of one person to another—­in other words, blood transfusion.  Modern doctors are proving themselves quite successful in its use.