Applications of Electronics in Medicine 53 



to pass a green light through the oxyhemoglobin solution ; the 

 amount of light able to pass is measured by a photoelectric 

 cell. The amount of light absorbed is proportional to the con- 

 centration of oxyhemoglobin, and thus it is possible to construct 

 a scale from which the percentage of hemoglobin can be rapidly 

 and accurately determined. Bell and Guthmann/ among others, 

 have devised a simple photoelectric hemoglobinometer. 



Photoelectric colorimeters can be used for turbidimetric de- 

 terminations just as readily as for colorimetric procedures. The 

 basis for the calibration of these methods, which depend on the 

 development of a uniform turbidity rather than a color, is a 

 solution of standard turbidity. Readings and results are obtained 

 just as with colored solutions. There are many applications 

 of photoelectric turbidimetric methods, but only their use in 

 penicillin assay will be mentioned here. Joslyn ^^ and Mc- 

 Mahan,^^ among others, used such methods. Rantz and Kirby ^^ 

 studied the action of penicillin on staphylococci by such a device. 



Nygaard ^^ studied the kinetics and phases of blood coagula- 

 tion by means of a photoelectric device. His method depends 

 on recording the amount of light transmitted through clotting 

 blood to a photoelectric cell. A continuous photographic record 

 of the diminution of the transmitted lisfht can be taken. 



•fc>' 



Photoelectric Plethysmography 



The basic principle of Leibel's method ^^ of measuring 

 peripheral blood flow is that the light intensity passing through 

 a finger or toe on which a beam of light is directed will vary 

 with the blood volume within the part, and will thus be an index 

 of the circulation through it. The^ emergent beam falls on a 

 photoelectric cell which changes any variation in the intensity 

 of the light into a corresponding variation in an electric circuit. 

 These electrical changes are amplified and then recorded with an 

 electrocardiograph. Two practical applications of this method 

 are the measurement of the pulse velocity by superimposing the 

 electrocardiogram on the tissue-circulation record, and the other 



