The purpose of this paper is to re-examine the spatial diffusion of Spanish influenza in Japan, which swept over the world three tunes from 1918 to 1921. According to the com-mon opinion they have said that the epidemic of Spanish influenza had not a clear diffusion process in Japan. But minutely examining the trend of the first outbreaks reported in “Influenza”, a report of the Spanish influenza, and “Statistics of the Causes of Death of the Empire of Japan”, the author believed to be doubtful to conclude so. For example, Fig. 2 and Fig. 3, showing the inter-prefectural diffusion process estimated from the peak month of the number of influenza deaths, suggest that the epidemic tended to diffuse from the western part to the eastern part in Japan.
Then, in order to investigate its diffusion process in detail, the author analyzed the monthly influenza mortality of each prefecture from July 1916 to June 1926, applying S-mode factor analysis. The 120 (the number of months)±46 (the number of prefectures) data matrix was subjected to factor analysis, and three factors with eigenvalues of greater than 1.0 were extracted (Table 1). Judging from Fig. 4 and Table 2 showing the correlations between some variables and factor loadings, the following interpretation seems to be possible.
Factor I, accounting for 78.8% of the total variance, is related to the contagious opportunity prescribed by the distance from the major ports (Kobe, Moji, Nagasaki, Shimonoseki and Osaka etc.) in the western part in Japan (Fig. 6), and distinguishes the Western Japan from the rest of the country. Factor II, accounting for 8.5% of the total variance, is related to the contagious opportunity corresponding to the hierarchical urban system, and distinguishes the urban areas from the other areas. Factor III, accounting for 7.9% of the total variance, is related to the factors promoting the prevalence of epidemic within the household (temperature, average number of persons per household, % of people under 15 years and over 60 years, personal income and number of doctors per 1, 000 persons), and distinguishes the Eastern Japan from the rest of the country.
Further cross correlations for lag values from -3 to +3 months between factor scores were calculated to clarify the time lead and lag relationship between three factors (Fig. 7). Consequently it turned out that there was not a marked time lag between Factor I area and Factor I area, but the epidemic could spread from Factor II area to Factor III area two months behind.
Therefore, on the basis of these cross correlations, the diffusion route could be presumed roughly as follows; The Spanish influenza diffused toward the east, invading through the major ports in the Western Japan, while it diffused into the urban areas, ‘moving down’ the urban hierarchy from Tokyo via Yokohama which was then the largest port in the Eastern Japan. And, two months later, the epidemic spread from the urban areas (especially Keihin region) to the Eastern Japan.
Above-mentioned result differs from the common opinion, but it suggests that there is a regular spatial order in the epidemic process of Spanish influenza in Japan.

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The Toyama Plain is noted for its high degree of paddy-field making, that is, the percentage of paddy-field within the cultivated land, is the highest among all the plains in Japan. The Toyama Plain is mostly alluvial plain, but spacious elevated fans are found near the foot of the mountains. Paddy-fields have been developed over the whole district, even in these elevated fans, accounting for the high degree of paddy-field making in the Toyama Plain as a whole. Spacious elevated fans are developed in Shizuoka, Kanagawa, Saitama, Nagano and other prefectures, but many paddy-fields can hardly be found in the elevated fans of these prefectures.
In general, the construction of irrigation canals (or reservoirs) is the basic element for the development of paddy-fields. The main purpose of this study is to make an inquiry into the factors that made the construction of irrigation canals possible in the elevated fans in the Toyama Plain, and also to throw some light on the kind of irrigation canals that have been built.
The Toyama Plain is drained by rivers, those as the rivers of Oyabe, Sho, Ida, Jinzu, Joganji, Kamiichi, Hayatsuki, Katakai, and Kurobe, and two-terraced or three-terraced elevated fans are found at the mouths of the valleys of all these rivers, with an exception of the Sho River. The present writer has carried out a detailed investigation on the configuration of the ground in the drainage area, seasonal variations in the amount of river water, the development of irrigation works, the conditions of irrigation, etc., concerning each of these rivers. Moreover, he has drawn up nine maps showing the elevated fans and irrigation canals of each river. The results of this study are summarized as follows:
It was in the Edo Period that, except for the highest part of the Tatenogahara elevated fan of the Oyabe River and a few others, and for the Osawano elevated fan, paddy-fields were developed in the elevated fans and irrigation canals were laid from the rivers. This is a surprising fact when we consider the history of irrigation in various districts of other prefectures in Japan. This is to be accounted for in part by the encouragements and assis-Lance given to the development of paddy-fields as a part of the agricultural policy of the Kaga Clan; but it is also partly attributable to the fact that there were rivers which made it possible, with the construction technique of the Edo Period, to bring irrigation canals in the highly elevated fans over comparatively short distances by utilizing the gradient of the valley bottom. Furthermore, the catchment area of the rivers between the mountains is not always wide enough to irrigate the paddy-fields located in the lower reaches of the rivers. However, since the district has heavy snowfall, during the period that requires the largest amount of water, that is, during the period of rice transplanting and its preparation, the rivers are supplied with abundant water from the melting snow, and there is always sufficient water available for the purpose of irrigation.
However, as we have seen in the conditions of the elevated fans along the rivers of Oyabe, Joganji, Karniichi, Hayatsuki, Katakaki, as well as the elevated fans of Junikanno and Tanayamano along the Kurobe River, there is always shortage of water in the irrigation districts during the period from the end of July through August, and the disputes among irrigation unions were of frequent occurrence. It is for this reason that the strict rules of traditional use of water were observed.
In recent years, as a result of the integration of irrigation canals and the construction of multipurpose dams, water use has been improved and progress has been noted for the methods of irrigation.

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