A Reflecting Photoelectric Erythema Evaluator

Abstract

Spectrophotometric color analysis is, of course, not new and is said to have been first used by Sheard and Sanford, of the Mayo Clinic, in 1928, for hemoglobin estimations. Their method was possibly an adaptation from the industrial field to the clinical laboratory, while mine is merely an attempt to make practical use of the same principle in the radiological field. Each method, of course, has its obstacles, the most important of which is the production of an unvarying base current and voltage i.e., wattage. Perfection in this is obviously impossible, but the storage battery when in good condition and freshly charged gets close enough for practical purposes. It may have a potentiometer across one of the end cells. Other solutions would be the constant wattage transformer or some of the V. T. voltage regulating devices now on the market. The principle of operation depends entirely on the current fluctuation produced in a barrier plane type photoelectric cell by the variations in intensity of luminosity striking its surface, due to the variations in skin shade or complexion which are reflected into the photoelectric cell by an especially designed illuminator. The fluctuation is read off on a microampere meter properly inserted in the circuit. At present, I am still using a 0 to 1 milliampere meter with 5,000 ohms in series with the P.E. cell, and an ordinary Pese Magnicell. By improving the quality of my units and increasing the resistances I will be able to get a response to much narrower differences in shading, even though slowing down that response. This is of no consequence in this instance as we do not require the instantaneous action so necessary to the proper functioning of other photoelectric devices: e.g., television, relays, etc. We are interested only in accurate needle deflection, and a few seconds lost in obtaining this necessary accuracy is unimportant. The wiring diagram (Fig. 1) is the one used in the instrument first constructed. It is undergoing almost daily alterations for obvious reasons. The illuminator must be finished a dull black inside and the bulbs should be frosted or color filters used. The sensitivity of response seems to be greater when working with as little illumination as possible. The light source must be well back of the P.E. cell and preferably multiple. In my instrument I am using three 3.8 v. flashlight bulbs. The hook-up is a modification of the Pese Universal Photoelectric set. I have retained the sensitive relay in order to test the P. E. cell and to demonstrate it to my colleagues. It also serves to protect the ma. meter, for the full output of the cell even through a 5,000 ohm series resistance would be too much current and might injure the ma. meter. A double pole double throw switch is used to cut in or out either the relay or the meter, and the switch is always left on the relay side after use.