There are other factors both social and economic which must not be omitted from an account of the influences of recuperation, namely the equipmental and other factors which produce social surplus. Disaster-stricken communities cannot survive unless their "surplus energy exceeds their needs." They cannot become normal until the social surplus is restored. The social surplus, according to Professor Tenney, is "merely the sum-total of surplus energy existing in the individuals composing a social group, or immediately available to such individuals."[144] It includes not only "bodily vigor" but "such material goods also as are immediately available for the restoration of depleted bodily vigor." It is not only physiological, as life energy, and social, as conditions of knowledge and institutional facilities, but also socio-economic, as equipment for the maintenance or restoration of physiological and social needs. In catastrophe bodily vigor may have been depleted, and material goods been consumed. No period of recuperation or rapid gain can ensue unless such equipment is in some degree replaced and a balance of social surplus restored. This is the _conditio sine qua non_ of recuperation, and of the transition from a pain-economy to a pleasure-economy,[145] after disaster. Certainly the maintenance of the standard of living demands it. The standard of living has been defined as the "mode of activity and scale of comfort which a person has come to regard as indispensable to his happiness and to secure and retain which he is willing to make any reasonable sacrifice." Following Professor Seager's association of the standard of living with population, the reduction of population in catastrophe of a certain character might conceivably operate to automatically heighten the standard of living, just as the growth of population often brings about its fall. But catastrophe often consumes great quantities of material goods and brings about a change in incomes and in occupations.[146] Seager notes that: Actual starvation confronts more rarely those belonging to the class of manual workers, but for them also under-nutrition is a possibility which prolonged illness or inability to obtain employment may at any time change into a reality. The narrow margin which their usual earnings provide above the bare necessaries of life, coupled with their lack of accumulated savings, makes them especially liable, when some temporary calamity reduces their incomes, to sink permanently below the line of self-support and self-respect.[147] [144] Tenney, Alvan A., "Individual and Social Surplus," _Popular Science Monthly_, vol. lxxxii (Dec., 1912), p. 552. [145] Patten, Simon N., _Theory of the Social Forces_ (Phil., 1896), p. 75.