"How far this change was due to other causes is a complicated question. The population may have suffered from foreign admixture during the troubled times that followed the death of Alexander. There were, however, many reasons against the view that these disturbances produced any appreciable difference of race. The presence of vast numbers of slaves, not members of households, but the gangs of toilers whom the increase of commerce brought into the country, pandered to a foolish pride that looked upon many kinds of honourable labour as being shameful and unbecoming to a free man. The very institution that made Greek civilisation possible encouraged idleness, luxury, and still worse vices. Unnatural vice, which in some States seems to have been positively encouraged, was prevalent among the Greeks to an almost incredible extent. It is hard not to believe that much physical harm was caused thereby; of the loss to moral strength and vigour there is no need to speak. The city-state, again, however favourable to the development of public spirit and a sense of responsibility, was doomed to fail in a struggle against the stronger Powers of Macedon and Rome. The growth of the scientific spirit destroyed the old religion. The more intellectual tried to find principles of conduct in philosophy; the ignorant or half-educated, deprived of the strong moral support that always comes from sharing the convictions of those abler and wiser than oneself, fell back upon degrading superstitions. In either case there was a serious loss of that spirit of self-sacrifice and devotion which a vigorous religious faith alone can bestow. Without such a spirit, as history proves conclusively, no nation or people can survive." [57] (b) _The Physical Catastrophe induced by Selfishness_ One of the physical catastrophes that probably most accelerated the fall of Greek civilisation was malarial fever. The parasite of this disease is carried from man to man by Anopheline mosquitoes. These insects, during the stage of egg, larva, and nympha, live in water, and afterwards, as developed insects, in the air. The breeding-grounds, where the eggs are laid, are shallow pools of stagnant water. For that reason the disease is most common in marshy country, and tends to disappear when the land is properly drained. Of this we have an example in England, whence malaria disappeared as the marshes were drained.