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.

No abstract

CUTE compression of the spinal cord or cauda equina caused by spontaneous epidural hematoma is relatively rare. Sadka 31 reviewed 1~ published cases and added two more. Schultz, et al., 32 Lougheed and Hoffmany and L6poire, et al., 2~ brought the total to 46 cases, to which we are now adding three cases. Case 1. A 79-year-old white woman was admitted to the San Jose Hospital on January ~8, 1961. At 4:00 a.m. that morning she had awakened with severe pain in the thoraco-lumbar region, which was followed by bowel incontinence. A few minutes later her right leg became so weak that she could not walk. Before the sudden onset of her symptoms the patient had been active despite mild cardiac insufficiency and diabetes mellitus. Examination. The bladder was distended to the umbilicus and catheterization was necessary. Neurological exanfination January g9, approximately 30 hours after onset of symptoms, revealed flaccid paralysis of both legs, with areflexia, and loss of all sensory perception below the level of T-10 bilaterally. Spinal puncture revealed a pressure of 100 mm of water, xanthochromic fluid, and a protein content of s mg%. X-rays of the lumbar spine were normal except for osteoporosis. Myelography revealed a complete block at the level of the disc space between T-11 and T-I~. Operation. Laminectomy was performed approximately 83 hours after onset of symptoms and 1~ hours after onset of paraplegia (}t.N.L.

Traditionally it has been thought that most boreal forest communities lack a significant input of biologically fixed nitrogen. Recent discoveries of nitrogen fixation by cyanobacteria associated with mosses have resulted in a re-evaluation of this view. While it is recognized that rates of nitrogen fixation in mosses can be highly variable, there is little understanding as to why this occurs. I monitored nitrogen fixation, using acetylene reduction, in wet lowland and dry upland boreal forest communities, in central Canada, over a growing season. At the peak of nitrogen fixation in mid summer, Sphagnum capillifolium had an 11 times higher rate of fixation than Pleurozium schreberi. Variation in canopy openness and precipitation had no effect on rates of fixation over the growing season. In P. schreberi fixation rates did not vary between sites. Temperature had a positive effect on fixation rates in both S. capillifolium and P. schreberi, but the effect was 4 times more pronounced in S. capillifolium. Seasonal rates of nitrogen fixation were estimated at 193 mg N m(-2) for S. capillifolium and 23 mg N m(-2) for P. schreberi. With moderate increases in climate warming, predicted increases in nitrogen fixation in S. capillifolium are sufficient to raise its decomposition rate. Increased temperatures may therefore act synergistically to change boreal systems from a sink to a source of carbon.

Biomass allocation patterns in plants are known to be affected by soil nitrogen availability. Since nitrogen availability can depress symbiotic nitrogen fixation, and nitrogen fixation can make plant growth independent of soil nitrogen availability but is energetically costly, it is unclear how allocation patterns in nitrogen-fixing species should respond to variation in soil nitrogen availability. We examined the effect of nitrogen source and concentration on the growth and allocation patterns in the nitrogen-fixing shrub Alnus viridis subsp. crispa (Aiton) Turrill. Plants were grown with either NH4+-N or NO3–-N at a range of low N concentrations, from 0 to 2 mmol·L–1, and either inoculated with Frankia or not. Plants without nodules had 25.l% lower biomass and had double the allocation to roots at all but the 2 mmol·L–1 nitrogen concentration. Even though nodulated plants increased growth with nitrogen concentration, allocation to roots as a fraction of total biomass did not vary in these plants, suggesting increased growth resulted from more efficient nitrogen acquisition. Allocation to roots was a significant predictor of plant growth in non-nodulated plants (r2 = 0.318, for linear least squares fit with log mass) but not for nodulated plants (r2 = 0.108). As nitrogen concentrations increased, allocation to nodules, specific nodule numbers, and the proportion of nitrogen fixed by the plants decreased, demonstrating a shift to soil nitrogen use.

No abstract