The Black Death, a severe epidemic that ravaged fourteenth-century Europe, has intrigued scholars ever since Francis Gasquet's 1893 study contending that this epidemic greatly intensified the political and religious upheaval that ended the Middle Ages.  Thirty-six years later, historian George Coulton agreed but, paradoxically, attributed a silver lining to the Black Death:  prosperity engendered by diminished competition for food, shelter, and work led survivors of the epidemic into the Renaissance and subsequent rise of modern Europe.

 

In the 1930s, however, Evgeny Kosminsky and other Marxist historians claimed the epidemic was merely an ancillary factor contributing to a general agrarian crisis stemming primarily from the inevitable decay of European feudalism.  In arguing that this decline of feudalism was economically determined, the Marxist asserted that the Black Death was a relatively insignificant factor.  This became the prevailing view until after the Second World War, when studies of specific regions and towns revealed astonishing mortality rates ascribed to the epidemic, thus restoring the central role of the Black Death in history.

 

This central role of the Black Death (traditionally attributed to bubonic plague brought from Asia) has been recently challenged from another direction.  Building on bacteriologist John Shrewsbury's speculations about mislabeled epidemics, zoologist Graham Twigg employs urban case studies suggesting that the rat population in Europe was both too sparse and insufficiently migratory to have spread plague.  Moreover, Twigg disputes the traditional trade-ship explanation for plague transmissions by extrapolating from data on the number of dead rats aboard Nile sailing vessels in 1912.  The Black Death, which he conjectures was anthrax instead of bubonic plague, therefore caused far less havoc and fewer deaths than historians typically claim.

 

Although correctly citing the exacting conditions needed to start or spread bubonic plague, Twigg ignores virtually a century of scholarship contradictory to his findings and employs faulty logic in his single-minded approach to the Black Death.  His speculative generalizations about the numbers of rats in medieval Europe are based on isolated studies unrepresentative of medieval conditions, while his unconvincing trade-ship argument overlooks land-based caravans, the overland migration of infected rodents, and the many other animals that carry plague.

Planter-legislators of the post-Civil War southern United States enacted crop lien laws stipulating that those who advanced cash or supplies necessary to plant a crop would receive, as security, a claim, or lien, on the crop produced.  In doing so, planters, most of whom were former slaveholders, sought access to credit from merchants and control over nominally free laborers--former slaves freed by the victory of the northern Union over the southern Confederacy in the United States Civil War.  They hoped to reassure merchants that despite the emancipation of the slaves, planters would produce crops and pay debts.  Planters planned to use their supply credit to control their workers, former slaves who were without money to rent land or buy supplies. Planters imagined continuation of the pre-Civil War economic hierarchy:  merchants supplying landlords, landlords supplying laborers, and laborers producing crops from which their scant wages and planters' profits would come, allowing planters to repay advances.  Lien laws frequently had unintended consequences, however, thwarting the planter fantasy of mastery without slavery.  The newly freed workers, seeking to become self-employed tenant farmers rather than wage laborers, made direct arrangements with merchants for supplies.  Lien laws, the centerpiece of a system designed to create a dependent labor force, became the means for workers, with alternative means of supply advances, to escape that dependence.

Solar ponds are bodies of water in which circulation is incomplete and there is a very high salt concentration that increases with depth.  This vertical change in salinity serves to trap heat because concentrated brine in the lowest water level acts as a collector and storage area for solar heat, while the less saline, lighter water at the upper levels provides insulation.  Heat is thus retained in the depths.

 

An artificial pond of this type has been constructed on the western shore of the Dead Sea in Israel in order to test its suitability as a source of low-grade heat for conversion into electricity.  An immediate threat to the success of the venture was the growth of algae.  Water in solar ponds must be kept maximally transparent to allow penetration of light to the deep storage area.  Therefore, any particles of matter in the water, such as algae cells, that scatter or absorb light will interfere with the collection of heat.

 

One proposed method of controlling the algae was the application of an algicide.  However, the Dead Sea is a closed body of water without any outlet and as such is very easily contaminated.  Extensive use of chemicals in numerous future full-scale solar ponds would lead to such contamination of the Dead Sea, which now enjoys a lucrative tourist trade.

A recent experiment has supplied a more promising method for controlling the algae.  To repress the algae cells' capacity for accommodating themselves to environmental changes, the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water.  This shock reduced the cells' ability to regulate the movement of water through their membranes.  They rapidly absorbed water, resulting in distortions of shape, increase in volume, and impairment to motility.  Their buoyancy adversely affected, the cells sank to the bottom of the pond, where they encountered the hot waters of the storage layer and were destroyed.  This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.