The article is a report on a collaborative study of three experienced teachers who reflected on the critical moments of their teaching experiences in a multi-age classroom in an elementary school in Western Canada. The focus in the article is on these critical moments in their teaching that brought about change and how these changes improved teaching practise. Using ‘reflective practise’ as a theoretical framework, the three teachers present a number of insights from their personal lives and from their practise to support the notion that the crucial factor in effective teaching is to be formal in learning how to become a ‘reflective practitioner’.

The influence of capsular and vascular invasion on prognosis was determined retrospectively in 52 children with Wilms' tumor. Local recurrence was more prevalent (0.26) in patients with rupture or capsular invasion than in any other group. Inadequate postnephrectomy irradiation or infiltration of the liver by nephroblastoma cells appeared to be predisposing factors in the development of these recurrences. Of the 26 patients with gross or microscopic vascular invasion, 13 developed metastasis. This proportion was significantly higher than in patients without vascular involvement (p < 0.05).

The present study was undertaken to define criteria for classification of chronic myelocytic leukemia in children and adolescents. From April, 1963 through July, 1971, 18 patients were available for study. Evaluation of the clinical, laboratory, and histopathologic features demonstrates three distinct subgroups: adult, juvenile, and familial chronic myelocytic leukemia. Parameters of most value in this distinction are the level of the white blood cell count, presence of thrombocytopenia or thrombocytosis, the bone marrow myeloid to erythroid ratio, and the presence or absence of well-defined malpighian corpuscles in the spleen. One patient with acute lymphocytic leukemia in remission manifested some unique features and may represent a fourth form of chronic myelocytic leukemia, resulting from previous chemotherapy or irradiation. The use of chemotherapy has not significantly prolonged survival in our patients. Two patients with familial chronic myelocytic leukemia are surviving in remission 9 years following splenectomy.

We propose an instability of a vortex array in the presence of axial normal-fluid flow in He II. This instability may be responsible for the influence of thermal counterflow on ion-trapping cross sections reported by Cheng, Cromar, and Donnelly.

This study was undertaken to explore the therapeutic and diagnostic value of splenectomy for children with acute myelocytic leukemia (AML) in remission. Of 29 consecutive untreated patients entering the study, 19 attained complete remission with mercaptopurine, vincristine, and 6-azauridine. Chemotherapy during remission consisted of mercaptopurine daily and cytosine arabinoside weekly. Because remission lasted 2 months or less in 5 patients, they did not undergo splenectomy. Fourteen patients underwent splenectomy while clinically in complete remission. Splenectomy was tolerated well with no major complications. Gross abnormalities of the abdominal organs were found in 11 patients. Histologic leukemia was found in 12 patients, most often in the spleen. Negro children did not respond to therapy as well as Caucasian children. Central nervous system (CNS) leukemia terminated clinical remission in 7 of the 14 patients. Four patients remain in initial CNS and hematologic remission for 18 to 24 months, and four others remain in initial hematologic remission for 16 to 18 months. These results suggest that in children with AML, splenectomy may influence the activity of leukemia and prolong the duration of remission.

We have measured the drift velocity of several positive impurity ions in He II in electric fields beyond the critical field for vortex-ring nucleation. The large differences in observed velocities for the various ions are satisfactorily accounted for by assuming that the ions differ in radius and hence in thermally activated escape rates from the vortex rings to which they are bound. These size differences are consistent with the low-field mobilities and are not consistent with the usual simple model for the ion structure.

We have developed a technique for introducing a variety of impurity atomic ions into liquid helium and measuring their mobility. We find that, in contrast with predictions of the "snowball" model of Atkins, the ion mobility depends on the atomic number of the core ion in a way that cannot be explained simply in terms of the mass of the ion. The relative mobility of $^{40}\mathrm{Ca}$ and $^{48}\mathrm{Ca}$ ions has been measured and is consistent with existing theories.