These pictures were made by a process known as "Kirlian photography" or electro-photography.
Kirlian photography as we know it was first discovered in 1939 by the Russian researchers Semyon and Valentina Kirlian. The process uses high-voltage, low-current electricity to expose film. The high-voltage electricity creates a corona discharge (by photo-ionization of the nitrogen in the air) around the object being photographed. Because the object is usually in direct contact with the film, the film accurately records the corona discharge from the object. Kirlian photography does not require a lens system or a camera.*
The images that occur from passing electricity through film are due in part to a small quantity of visible light in the corona discharge. A portion of the exposure comes from an unseen segment of the electromagnetic spectrum in the ultraviolet wavelengths. Additionally, there appears to be exposure that comes from the depth of electrical penetration of the films different emulsion layers and base. When I am working with the Kirlian process I begin by taking plant forms or mechanical objects (capable of conducting electricity) and I make intuitive arrangements of the objects. After I have found a composition that I like I tape the objects in place on to a piece of Plexiglas. The Plexiglas has holes drilled into it that will allow me to register it to the exposure unit with a copper plate that is used to hold the film in place and to conduct electricity. This allows for a certain amount of precision when working in total darkness. Regardless of the amount of preparation I do before the exposure there is still a bit of serendipity involved. In my experiences with this process not a single object has exposed the same way twice.
Kirlian photography has been thought by some to show the power to diagnose human or other biological entities physical and mental states. Unfortunately, there does not appear to be any serious scientific results (due to the stringent requirements of scientific method) in favor of this process as a diagnostic tool.
I think of these photographs as making the invisible visible. They make references to the electro-chemical processes required of living beings to exist. To my own mind they even speak to the current theory that all life on earth began in a primordial soup literally sparked to life by atmospheric lightning. At the very least I find them simply fascinating and beautiful to look at.
* This passage is taken pretty much verbatim from the book "Kirlian Photography - A Hands on Guide" by John Iovine.