Some of the rheological properties in the blood circulation affecting hemodynamics were discussed.
1) The viscosity of blood varies according to diameter of vessel, flow velocity and hematocrit value, though the viscosity of serum or plasma is almost constant. This anomalous viscous properties of blood may be due to a) mutual coherence of red blood cells, b) wall effect or existence of plasma layer (1-3u in width) resulting from the axial drift of red blood cells and c) orientation and deformation of red cells in the sheared blood. The curve representing the relationship between rate of shear and shearing stress tends to be convex to the latter axis when blood is sheared low. However, at high rate of shear the curve approaches to asymptote.
2) Pressure-volume curve of great vessels shows an elastic hysteresis. Thus, blood vessels are assumed to have visco-elastic anisotropic and non-homogeneous walls. Elasticity modulus of arterial blood vessels in vivo may also vary with the state of muscular activity in the wall, vascular diameter and mural thickness. However, the deviation from linearity seems to be less than 5 per cent in arterial system. The true phase velocity of pulmonary arterial pressure wave in man free from pulmonary hypertension is estimated to be nearly 200 cm per second.
3) Pressure pulse waves show breaking phenomenon also in the pulmonary arterial system as well as in the systemic. This marked distortion of arterial pressure pulse waves transmitted along the artery is explained by a) numerous small pressure reflections, b) non-uniformity of the system, and c) dispersion of the pressure harmonics with different phase velocity.
Assuming that visco-elastic properties of the vascular system are linear, it is still not so erroneous to estimate approximation in praxis, so far as blood velocity is high and blood vessel is large enough for the measurement.

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Each of two systems of the accommodation and the vergence eye-movement in human eyes is considered to be a feedback control system. It is well known by two phenomena, the accommodation-vergence and the convergent accommodation, that the functions of these control systems are closely related each other. In this paper, the experimental results are shown which reveal dynamic characteristics of the systems of accommodation-vergence and convergent accommodation. It is assumed that both systems are of a linear dynamical system.
By the use of opto-electronic apparatus and targets which moved back and forth, the responses of accommodation-vergence and convergent accommodation to the target motion were detected. The details of the apparatus and the experimental results are given.
Although the present results are unsatisfactory to clarify the control mechanisms, indicial and frequency responses suggest that the dynamic and the static characteristics are quite different between two systems. For the accommodation-vergence, a reasonable model which realizes the characteristics of its control mechanism can be introduced from the view point of control system analysis. On the other hand, it is supposed that the mechanism of the information processing in the convergent accommodation is different from that in the accommodation-vergence, and further response waveform analysis will be necessary to clarify its function.

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A model of activities of a single neuron is presented. It has a large number of input lines and is composed of three main parts : an adder, a filter and a threshold element. Under some reasonable assumptions, the output of the filter can be treated as a random process, and the first passage times (FPTs) for this process correspond to the intervals of successive output pulses from the model.
Two kinds of random processes are examined. The first is known as the Erlang's system in telephone traffic theory. The mathematical expression of the probability density function (pdf) of the FPTs is obtained for this process. The second process is resulted from the filtering of the input random pulse train by a single stage RC filter. The FPTs are obtained by the digital computer simulation.
The main results obtained are as follows:
1) The output pulses form a renewal process, and the output process is completely characterized by the distribution of pulse intervals.
2) The pdf of output pulse intervals is expressed as the sum of several terms of exponential functions.
3) When the input pulse density increases, the pdf tends to that of a Gamma distribution.
4) When the input pulse density decreases, the pdf tends to that of an exponential distribution.
5) The mean pulse density input-output characteristics of the model are nearly linear when the threshold is low, and become highly nonlinear when the threshold grows higher.

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Artificial hearts which we now use are of air-driven sac type and driving device is fluid amplifiers with electro-pneumatic converter.
A blood handling part of artificial heart has a siliastic ventricle of 47 m_l., which is in an acryl outer case of 95 m l. The outer case is connected to the driving device with a vinyl tube of 8 mm. in diameter and 2 m. in length.
A driving device consists of a cardiac synchronizer, an oscillator, an electro-pneumatic converter and two power fluid amplifiers.
The cardiac synchronizer produces synchronized electric pulses by an electro-pneumatic converter. The electro-pneumatic converter is bistable wall attatchment type and has an electro-magnetic relay at a control part of the fluid amplifier. It converts electric pulses into pneumatic signals of 0.1 kg/cm².
The pneumatic pulses drive final fluid amplifiers which consist of two types of monostable fluid amplifier (left and right) and produce pneumatic driving pulses. The air pressure of the output pulses is about 0.3 kg/cm² and its flow rate is about 30 l/min in the left side device and 0.05 kg/cm², 30 l/min in the right side device.
Characteristics of this control device are (1) perfect synchronization with natural heart, (2) good fitting to Starling's law, (3) adequate shape of driving pulse wave and (4) long durability and high reliability.
A driving device for the artificial heart with a pure fluidic oscillator and a pulse shaping amplifier is also developed. This device gives pure pneumatic instrument.
The newest device is the pneumatically actuated valve. This may produce many new method of fluid control.

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