1. A DEVICE FOR DETERMINING THE INDIVIDUAL AND AVERAGE CONTENT OF LIGHT ABSORBING FLUID IN A PLURALITY OF FLUID SAMPLES, COMPRISING MEANS DEFINING A PAIR OF CHAMBERS, A PHOTO-SENSITIVE DEVICE IN EACH SAID CHAMBER, MEANS FOR DIRECTING LIGHT THROUGH EACH OF SAID CHAMBERS TO FALL ON THE SAID PHOTO-SENSITIVE DEVICE THEREIN, AND A VALVE HAVING FIRST FLOW-DIRECTING MEANS ACTING OVER A PLURALITY OF SINGLE SAMPLE POSITIONS TO DIRECT INTO A FIRST ONE OF SAID CHAMBERS EACH OF SAID PLURALITY OF FLUID SAMPLES IN TURN, AND SECOND FLOW-DIRECTING MEANS ACTING SIMULTANEOUSLY TO DIRECT THE REMAINDER OF SAID PLURALITY OF FLUID SAMPLES INTO THE SECOND OF SAID CHAMBERS, SAID FIRST FLOW-DIRECTING MEANS ACTING IN A CONBINED-SAMPLE POSITION TO DIRECT A NEUTRAL FLUID INTO ONE OF SAID CHAMBERS AND SAID SECOND FLOW-DIRECTING MEANS ACTING SIMULTANEOUSLY TO DIRECT A COMBINATION OF ALL SAID PLURALITY OF FLUID SAMPLES INTO THE OTHER CHAMBER, AND MEANS CONNECTED TO SAID PHOTO-SENSITIVE DEVICES FOR COMPARING THE RESPONSES OF SAID DEVICES TO DETERMINE, IN SAID SINGLE-SAMPLE POSITIONS OF THE VALVE, THE INDIVIDUAL LIGHT-ABSORBING PROPERTY OF EACH SAMPLE IN TURN RELATIVE TO THE LIGHT-ABSORBING PROPERTY OF SAID REREMAINDER OF THE SAMPLES, AND TO DETERMINE IN SAID COMBINED-SAMPLE POSITION OF THE VALVE, THE AVERAGE LIGHTABSORBING PROPERTY OF THE SAMPLES.