The Black Death, originating in Asia, arrived in the Mediterranean harbors of Europe in 1347 CE, via the land and sea trade routes of the ancient Silk Road system. This epidemic marked the start of the second plague pandemic, which lasted in Europe until the early 19th century. This pandemic is generally understood as the consequence of a singular introduction of Yersinia pestis, after which the disease established itself in European rodents over four centuries. To locate these putative plague reservoirs, we studied the climate fluctuations that preceded regional plague epidemics, based on a dataset of 7,711 georeferenced historical plague outbreaks and 15 annually resolved tree-ring records from Europe and Asia. We provide evidence for repeated climate-driven reintroductions of the bacterium into European harbors from reservoirs in Asia, with a delay of 15 ± 1 y. Our analysis finds no support for the existence of permanent plague reservoirs in medieval Europe.

Plague, caused by the bacterium Yersinia pestis, can spread through human populations by multiple transmission pathways. Today, most human plague cases are bubonic, caused by spillover of infected fleas from rodent epizootics, or pneumonic, caused by inhalation of infectious droplets. However, little is known about the historical spread of plague in Europe during the Second Pandemic (14-19th centuries), including the Black Death, which led to high mortality and recurrent epidemics for hundreds of years. Several studies have suggested that human ectoparasite vectors, such as human fleas (Pulex irritans) or body lice (Pediculus humanus humanus), caused the rapidly spreading epidemics. Here, we describe a compartmental model for plague transmission by a human ectoparasite vector. Using Bayesian inference, we found that this model fits mortality curves from nine outbreaks in Europe better than models for pneumonic or rodent transmission. Our results support that human ectoparasites were primary vectors for plague during the Second Pandemic, including the Black Death (1346-1353), ultimately challenging the assumption that plague in Europe was predominantly spread by rats.

A nerve membrane model with a two-state pore system was investigated by computer simulation in the uniform (space-clamped) case. Both sodium and potassium conducting pores were modelled, each pore having four independent gates which switched randomly between the open and the closed position, governed by the assumed rate constants. Each pore conducted only when all the gates were open. The model was based upon the Hodgkin-Huxley equations for the giant axon in squid, and in the limit of an infinite number of pores it was identical to these. The firing behaviour of this model as a function of the number of pores and the injected current were investigated. The mean firing frequency and the distribution of interspike intervals were mainly used in the presentation of the results. It was found that for pore numbers less than about 20 000 the main effects due to a finite number of pores were a lowering of the current threshold for firing and a more linear frequency current relationship relative to that of the original H-H equations. For higher pore numbers an increase in the current threshold and a pronounced burst firing close to the threshold were found.

SUMMARY1. Pulsed bidirectional Doppler-ultrasound equipment was used to measure changes in blood velocities in the femoral artery on a beat to beat basis for consecutive contraction and relaxation phases during voluntary rhythmic exercise of the quadriceps muscle group in man.2. Rapid and large fluctuations of blood velocities were found, being high during relaxation and low during contraction phases. At the onset of contraction phase, negative velocities were present, indicating retrograde flow. During the rest of the contraction phase, forward flow occurred comparable to the resting flow level even at high loads.3. Estimated maximal flow to the whole leg during relaxation phase, calculated from these blood velocity measurements and vessel diameter (measured with echoultrasound equipment with high resolution) was in two of the subjects 3-32 1 min-' (female) and 5.97 1 min-1 (male). When using computer tomography to estimate the volume of the quadriceps muscle group, the calculated maximum flow to this muscle group was 243 (female) and 257 (male) ml min-' 100 ml muscle-'. The time-averaged flow during exercise to the whole leg was 1-51 1 min-' (female) and 2'47 1 min-(male). The calculated time-averaged flow to the quadriceps muscle group was 101 (female) and 98 (male) ml min-' 100 ml muscle-'.4. The duration of post-contraction hyperaemia following such rhythmic exercise of up to 6 min duration and up to 75 % maximum voluntary contraction was never in excess of 150 s.

Every 5th year since 1920 the heights and weights of all Oslo schoolchildren (aged 7 to 18 years) have been measured, and the measurements processed centrally. For ages between 8 and 14 the mean height increased by about 4 cm per decade between 1920 and 1940 for both sexes. A drop of about 1.5 cm occurred during World War II, followed by a rapid catch-up. Since 1950, height has increased only moderately. A weight increase of between 1.5 kg (8 years old) and 3.5 kg (13 years old) per decade before 1940 was followed by a drop during the war equivalent to somewhat less than one decade's gain. A rapid catch-up after the war was followed by a slight decrease since 1950, especially for ages above puberty. A stable difference in the social composition of the eastern and western districts of Oslo allowed comparison of the trends for lower and higher social strata. Before the war, children from higher strata were taller than children from lower strata, but this difference has now practically disappeared. Children from the higher strata weighed more until about 1955, but later those from the lower strata weighed markedly more, especially during adolescence. The difference in menarcheal age between social strata was examined in 1928, 1952, 1970 and 1975. The time trend parallels that for weight: menarcheal age was lowest among higher strata until the 1950s, but after that the lower strata experienced the lowest menarcheal age.