On the basis of some results of our experiments, the recent progress in biological research of aging mechanism in multi-cellular organism is reviewed. Comparison of the life span of various organisms of different phyla indicates/that definite length of the life span is found in animals supported by the post-mitotic critical cells. In mouse and fish, age related changes in DNA structure in the post mitotic cells were demonstrated in vitro by templete activity of DNA of cells at different ages. In old cultured chick fibroblasts, cell surface was coated with hyaluronic acid. From various facts, important role of extracellular compartments in aging of organism is also suggested.

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Our project team had performed field studies on the epidemiology of stroke in the two villages. For four years of observation after the initial examination, the new cases from stroke were 75 in a village and 54 in another village. Among these new cases, we got 34 cases of cerebral haemorrhage and 48 cases of cerebral infarction, who had the complete information regarding the factors of the occurrence of stroke. For each of the cases, an individual who had the same sex, age, occupation and living place as the corresponding case was selected as the control at random from each population. In this way, 34 pairs were formed for cerebral haemorrhage and 48 ones for cerebral infarction. Relative risk for cerebral haemorrhage and cerebral infarction was estimated by the method of case-control study with matching.
The risk from cerebral haemorrhage was 5.00 times as many for the persons with 160mmHg systolic blood pressure or over (systolic hypertensives) as for those with systolic blood pressure less than 160mmHg (non-systolic hypertensives), 4.60 times as many for those with 95mmHg diastolic blood pressure or over (diastolic hypertensives) as those with diastolic blood pressure less than 95mmHg (non-diastolic hypertensives), 3.40 times as many for those with high R of the ECG pattern as those without high R and 3.20 times as many for those with hypertensive findings of eye-ground as for those without hypertensive findings.
The risk from cerebral infarction was 3.33 times as many for the persons with subjective symptoms (brain) as for those with no subjective symptom, 2.88 times as many for systolic hypertensives as for non-systolic hypertensives and 2.50 times as many for diastolic hypertensives as for non-diastolic hypertensives.
Stroke is considered to have a multivarable causality. Where several factors act simultaneously, and perhaps interact, to influece the occurrence of stroke, and where some of those factors are intercorrelated, a multivariate analys is isrequired. In the second analysis, we estimated the risk factors by the discriminant function analysis, using thesame pairs that we examined by the case-control study with matching.
It was found that the occurrence of cerebral haemorrhage was most remarkably influenced by systolic blood pressure, being influenced by the following six factors: ST-T changes of the ECG pattern, diastolic blood pressure, arteriosclerotic findings of eye-ground, hypertensive findings of eye-ground, high R of the ECG pattern and family history. But serum total cholesterol occupied the fifth place and did not appear to develop cerebral haemorrhage.
The occurrence of cerebral infarction was influenced by the following four factors: systolic blood pressure, arteriosclerotic findings of eye-ground, hypertensive findings of eye-ground and subjective symptoms (brain).
It is clear that hypertension is the most common and potent precursor of cerebral haemorrhage as well as cerebral infarction and control of hypertension seems to be indispensable to prevention of these diseases in the rural Japanese. Neither the persons with obesity nor those with hyperlipidaemia developed stroke in this study. It was considered that this was racial characteristics in today's Japan. And we should fix the attention on the fact that subjective symptom (brain) was one of the important risk factors for cerebral infarction. So we hope that clinical symptoms which is related to transient focal cerebral ischaemia will be taken in detail in population studies on stroke.

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