With 4 FiguresPneumocephalus has been of special interest Go clinicians for at least 80 years, and most neurosurgeons have had experience with one or more cases, yet a total of only 284 reported cases since 1884 was found in an extensive review of the literature. The writer became particularly interested in this subject because of personal experience with a ease in which no etiology was found in spite of 6 years' observation and an autopsy examination (case 1). Survey of the literature was conducted for similar cases but none was found. Meanwhile, 10 other patients with pneumocephalus were encountered, making a total of ii cases studied by the author. Only two reports of larger case series were found in the literature, rfi6nnis and J["rowein s~ reported 14 cases, and Rizzoli, Hayes and Steelman l~ reported 12 eases. Moreover, relatively few of the articles reviewed were devoted to detailed study of pneumocephalus. Historical AspectsAccording to Froment, Gonin and Viallier ~s the first writer to use the word "pneumatocele" was Chevance de Vassy, In 1852 he used this term to describe a ease of extraeranial pneumocephalus. In 1873 Wernher ~2~ described another case of spontaneous extraeranial air accumulation secondary to ehaages ia the mastoid cells. He found 11 similar cases ia the literature from 1777 to 1873. These were described under such terms as "emphysema capitis", "paeumatoeele cranii", etc.

Top predators can provide fundamental ecosystem services such as nutrient cycling, and their impact can be even greater in environments with low nutrients and productivity, such as Arctic tundra. We estimated the effects of Arctic fox (Vulpes lagopus) denning on soil nutrient dynamics and vegetation production near Churchill, Manitoba in June and August 2014. Soils from fox dens contained higher nutrient levels in June (71% more inorganic nitrogen, 1195% more extractable phosphorous) and in August (242% more inorganic nitrogen, 191% more extractable phosphorous) than adjacent control sites. Inorganic nitrogen levels decreased from June to August on both dens and controls, whereas extractable phosphorous increased. Pup production the previous year, which should enhance nutrient deposition (from urine, feces, and decomposing prey), did not affect soil nutrient concentrations, suggesting the impact of Arctic foxes persists >1 year. Dens supported 2.8 times greater vegetation biomass in August, but δ15N values in sea lyme grass (Leymus mollis) were unaffected by denning. By concentrating nutrients on dens Arctic foxes enhance nutrient cycling as an ecosystem service and thus engineer Arctic ecosystems on local scales. The enhanced productivity in patches on the landscape could subsequently affect plant diversity and the dispersion of herbivores on the tundra.

Laminaria saccharina Lamour. sporophytes were grown in enriched and synthetic media through a range of nitrate concentrations, There was an approximately linear relationship between growth and nutrient concentration up to 10 μ substrate concentration. The half‐saturation constant (K2) was ca. 1.4 μ NO3‐. The internal levels of NO3‐ increased at substrate concentrations above 10 μM b>3‐ and reached levels several thousand times higher than the surrounding medium. Thus there is evidence for luxury consumption of NOsb>3‐. The chlorophyll content and photosynthetic capacities of plants also increased with increasing external NO3‐ The ecological implications of this work are considered.