Selectivity in regeneration of the oculomotor nerve in the cichlid fish, Astronotus ocellatus

It has long been considered a general rule for nerve regeneration that the reinnervation of skeletal muscle is nonselective. Regenerating nerve fibers are supposed to reconnect with one skeletal muscle as readily as another according to studies covering a wide range of vertebrates (Weiss, 1937; Weiss & Taylor, 1944; Weiss & Hoag, 1946; Bernstein & Guth, 1961; Guth, 1961, 1962, 1963). Similarly, in embryogenesis proper functional connexions between nerve centers and particular muscles are supposedly attained, not by selective nerve outgrowth but rather through a process of ‘myotypic modulation’ (Weiss, 1955) that presupposes nonselective peripheral innervation. Doubt about the general validity of this rule and the concepts behind it has come from a series of studies on regeneration of the oculomotor nerve in teleosts, urodeles, and anurans and of spinal fin nerves in teleosts (Sperry, 1946, 1947, 1950, 1965; Sperry & Deupree, 1956; Arora & Sperry, 1957a, 1964)

Micrometre-scale refrigerators

A superconductor with a gap in the density of states or a quantum dot with discrete energy levels is a central building block in realizing an electronic on-chip cooler. They can work as energy filters, allowing only hot quasiparticles to tunnel out from the electrode to be cooled. This principle has been employed experimentally since the early 1990s in investigations and demonstrations of micrometre-scale coolers at sub-kelvin temperatures. In this paper, we review the basic experimental conditions in realizing the coolers and the main practical issues that are known to limit their performance. We give an update of experiments performed on cryogenic micrometre-scale coolers in the past five years

Ikey Angotisiak Bolt (1894-1981)

The arrival of the Canadian Arctic Expedition (1913-1918) was of profound influence in exposing the Copper Eskimo of Coronation Gulf and Victoria Island to the culture, lifestyle, and technology of Caucasian North America. And Ikey Bolt was one of the most outstanding members of that party. He was an Alaskan Eskimo who, far from his native land, made his home among these people and built a reputation for integrity and community service that will not easily be forgotten. Ikey Bolt was born in Point Hope, Alaska, on 19 January 1894, in a whale-hunting culture that provided him with stories of the hunt with which he would regale his listeners all his life. Recruited in his late teens as an interpreter for the Canadian Arctic Expedition, he made his initial trip to Canada. ... The best appreciation of Ikey Bolt's contribution to the region can only be understood in the context of the times. Here is a native Alaskan whose people had been long exposed to the influence of southerners in the traumatic whaling era, a period of mixed blessings if ever there was one. In joining the Canadian Arctic Expedition he made contact with a people who were literally just emerging from the Stone Age, a people who had no steady contact with explorers until the Canadian Arctic Expedition arrived. They hunted with harpoons and with bows and arrows, and they had no recourse to any products of southern technology except for bits of iron traded with distant neighbours who had obtained them from abandoned ships. The introduction of a different way of life - new methods of trapping animals to be exchanged for trade goods - had all the potential for cultural devastation and the erosion of even the best of their indigenous philosophy. But the presence and influence of natives who had themselves survived similar upheavals and yet maintained a strong sense of spiritual and cultural values made a profound difference. ..

Henry George Cook

This profile describes the life of Henry George Cook, sometime Anglican bishop of Mackenzie. Henry Cook began his ministry in 1935 in Fort Smith, N.W.T., carrying out clerical duties including teaching school and the study of the Slavey language, used by the Indian population in that area. In 1943 he moved to Toronto and in 1949 became superintendent over the Anglican mission schools in the provinces and the two territories. Bishop retired in 1974 at the age of 68. However, Bishop and Mrs. Cook were not finished with the North. Cook was invited by Commissioner Stuart Hodgson to assist in the setting up of what was to become the Prince of Wales Northern Heritage Centre which was opened in 1979. "The later history of the church's life, together with the development of missions down the Mackenzie area, would not be complete witout an acknowledgment of the devotion, commitment and concerned oversight expressed through the life and ministry of Henry George Cook, bishop of Mackenzie.

Myotypic Respecification of Regenerated Nerve-fibres in Cichlid Fishes

In man and other mammals normal motor co-ordination is not restored, as a rule, after regeneration of a severed peripheral nerve-trunk (Sperry, 1945). The random misdirection of regenerating fibres into foreign muscles tends to prevent normal dissociated action within the re-innervated musculature. In contrast, larval amphibians have been found to show excellent recovery of motor function in the form of ‘homologous or myotypic response’ (Weiss, 1936, 1941) following the cutting and regeneration of limb-nerves, limb transplantation, and the cross-connecting of limb nerves to foreign muscles. Similarly, good restoration of muscle co-ordination has been observed in the pectoral fin of adult teleost fishes (Sperry, 1950, 1956)

Seasonal occurrence of xylem embolism in sugar maple (Acer saccharum)

Journal ArticleXylem embolism, the reduction of water flow by air-filled vessels, was measured in a stand of 5- to 8-year-old sugar maple (Acer saccharum Marsh.) saplings growing in a nursery bed in northwestern Vermont. Embolism was quantified as percentage loss in hydraulic conductivity of trunk and branch segments relative to maximum values obtained by removing air from vessels by repeated high pressure (173 kPa) perfusions. Ten segments per tree were cut from 6 trees for each of 11 measurement periods spaced at roughly monthly intervals from May 1986 to June 1987