Circulation of blood as a physical phenomenon could be analyzed by the application of the principle of fluid dynamics. Because blood is noncompressible viscous fluid and blood vessels are viscoelastic tube and the motion of blood in blood vessels is pulsatil and quite complex, there can be found no analogy in physics and engineering.
Theories and experiments of the field has been quite primitive and had serious approximations till recent decade. Modern development of medical electronics and biological engineering brought much progress in the theories and experiments of hemodynamics. The author intends to present necessary conditions and limitations of these theories and methods from the biological, stand point to the non-medical readers.

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Phonocardiograph has made great progress in regard to the graphic registration for the auscultatory phenomena as percieved by the human ear. However, some problems that are essential to phonocardiography especially its standardization have remained unsolved.
The problems are :
First, to calibrate a microphone accurately under the similar conditions to actual use; Second, to analyze the frequency-intensity characteristics of heart sounds and murmurs by using the calibrated microphone;
Third, to design the filter system based upon the results obtained by the above method.
Current situation of above problems and of others in phonocardiograph is reviewed.

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The authors discuss functioning mechanism of a receptor from the viewpoint of engineering. The distinctive features of receptors are :
1) high sensitivity, 2) responsiveness to a wide range of stimulus intensity, in accordance with Weber-Fechner's law, and 3) readiness to respond to a quick change in the intensity of stimulus as compard with a slow change, thus enabling a living system. to be rather sensitive to dynamics of environments than to statics.
Though the functioning mechanism of receptors is generally obscure, a receptor potential, slow change of cell membrane potential evoked by stimulus, may possess a significance in the function of some types of receptors.
The authors simulated the receptor potential generated by a lateral eye of Limulus to a combined model of electrical characteristics of cell membrane and photo-chemical reaction. The model possesses similarities in several aspects which are well known in the physiology of the receptor potential, i. e., 1) time course of the receptor potential, 2) relation between the intensity of stimulus and the receptor potential, 3) effect of concentrations of sodium and potassium ions and that of depolarizing current on the receptor potential, and 4) characteristics of summation, depression, refractoriness and adaptation.

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A mathematical model of the system of clinical medicine is proposed. The model is composed of 3 vector variables, which represent inner state of an organism, symptom and treatment as functions of time and of their interrelationships.
The inner state is governed by an inner mechanism of the organism and assumed to be unobservable in itself. However, it reveals itself transformed into symptoms which are observable by medical means. An inference of the inner state derived from the symptom is called a diagnosis. A medical means which is applied to the organism to bring the inner state of disease to that of health is called a treatment.
The model is restricted to a linear dynamical system with a discrete time variable for the sake of simplicity. Especially a stationary system in which the structure of the system does not vary with time is considered in detail along the line developed in the theory of linear dynamical system.
Several concepts such as diagnosability, treatability, simulation of a system and optimal treatment are introduced and their mathematical properties are investigated in some detail.
The correspondence between the present model and the actual case is discussed, bearing upon further development of the model.

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As a reliable and convenient method for presenting calibration voltage and a horizontal and vertical reference frame for vectorcardiogram, there has been developed a new technique which consists of superimposing a circle of 1 mV in radius and a cross orienting to the horizontal and vertical axis on vector loops.
A sinusoidal wave generated in a battery-operated Terman oscillator (Wien bridge) is divided by resistors and capacitors of the load into two waveforms having an equal amplitude (2 mV p-p) but a phase difference of 90 degrees between them. (The apparatus was manufactured for the trial by courtesy of Nihon Koden Co., Tokyo.) Each of the two outputs is fed through preamplifiers into the horizontal or vertical axis, respectively, of a vectorcardiograph equipped with three cathode ray oscilloscopes. If gains of both of the horizontal and vertical axes are exactly equal, as required for recording vector loop, a circle is expected to be observed on the vectorcardiograph, and if not an ellipse. Accordingly, adjustment of gains will be fairly easy and exact.
By grounding input of one axis and feeding the above-described sinusoidal wave (2 mV p-p) to another, a vertical or horizontal line, a segment, is observed. Vector loops, the circles and the horizontal and vertical segments are superimposed upon each other on picture. Superimposing process is carried out by repeating exposure without winding up the film, or by flashing the beam of cathode ray oscilloscope each time for each of the component, keeping the diaphragm of camera open.
The vectorcardiogram thus recorded has the following advantages : 1) It makes easy and direct visualization of the amplitude of vector loops. 2) The circles also serve as a reliable standard for accurate measurement of the amplitude of loops. 3) It gives a reliable frame of horizontal and vertical axes for determining direction of the initial or maximal axes.

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Construction of a climatometer, a type of “effective temperature” thermometer, and the experimental results with it are described. In order to improve the climatometer, resource with skin surface and body temperature variation in males by environmental heat condition cited from a paper, “Electrical Analog Simulation of Temperature Regulation in Man”, by R. J. Crosbie, J. D. Hardy and E. Fessenden is introduced.
The climatometer directly indicates in degrees cetigrade a measure derived from environmental temperature, namely, “equivalent temperature” felt by human body. The effective temperature is a function of air temperature, relative humidity, air velocity and heat radiation from distant heat sources. The climatometer comprises a new special sensitive element whose surface temperature is affected by any change of each factor described above, and a measuring part which indicates the temperature of the sensitive element.
In the paper described by R. J. Crosbie et al., skin and body temperature in man were analyzed by an analog computer applied to a one-dimensional physical model, namely, the slab model in place of human body. The slab model consisted of three layers and each was assumed to have a temperature which was constant throughout the thickness. For each layer, a separate one-dimensional heat flow equation was applied which contained_time as the sole independent variable. As the solution, graphical representation of skin and body temperatures versus ambient temperature was obtained. The data offer valuable_information in improving and developing a climatometer.

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Ballistocardiography is concerned with recording the movement of human body and deriving physically, physiologically, clinically pertinent information from the recording. The movement of the body on a table is exerted by the forces in the heart and aorta produced by the blood emitted from the heart. These forces are spatially distributed throughout the body corresponding to the phasses of cardiac cycle, and transformed into the motion of the table. Therefore, the human body as an oscillating system, i. e., mechanical characteristics of the body as well as those of the table should be first investigated in order to, make use of ballistocardiography.
The authors investigated the human body as an oscillating system by analyzing the : responses of the body to external forces, and simulated the combined system of body and table to a three-dimensional system with the the aid of an analog computer. It was assumed that the human body is rigid and possesses springs and dampers on its surface.
The experimental results indicate that the natural frequencies of the body in free-motion are 5 cps, and 5 cps and 10 cps and that the damping ratios are O. 1, 0.1 and 0. 17 in the left to right, head to foot and back to forward directions, respectively. The results of simulation suggest that the increase in the degrees of freedom of the table is desirable for better table-body characteristics.

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