THE PRESENT STATUS OF THE GERM-CELL PROBLEM IN VERTEBRATES

(i) Morphological studies relating to the origin and differentiation of the definitive germ cells in vertebrates have, as indicated, resulted in conflicting views. In many instances two or more competent investigators who have studied the same form have reached different conclusions. (2) Some contend that the germ cells are set aside from the soma during the early stages of embryonic development, and that these alone serve as the progenitors of the functional sex cells. (3) Others recognize an early differentiation of sex cells but hold that these are supplemented by others produced from the somatic epithelium of the gonad in late embryonic or post-embryonic stages. (4) Another group recognizes the early differentiated cells as germ cells but contend that these all degenerate and that the definitive ones are formed from the germinal epithelium. These degenerating germ cells are believed by certain authors to be a phylogenetic recapitulation of the condition in lower forms. (5) Finally, yet another group contends that the so-called primordial germ cells are not germ cells at all but are enlarged cells in some stage of mitosis or in some specific metabolic phase. This group believes that all germ cells are derived from the somatic cells of the germinal epithelium. (6) Experimental work supports the view that the primordial germ cells, which are recognized early, are the progenitors of the definitive sex cells. When these primordial germ cells are prevented from reaching the site of the developing gonad the individual fails to develop sex cells, although a sterile gonad and its associated structures may develop. (7) I suggest that the observed proliferation of germ cells from the germinal epithelium, reported by numerous investigators, can be interpreted in another way by a thorough study of the enlarged germ cells in relation to the epithelium. It seems probable that the cells of the epithelium, which form functional sex elements, are not and never were a part of the mesothelial covering, but are cells which were segregated early, and are merely stored in the epithelium.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74677/1/j.1469-185X.1945.tb00313.x.pd

Meeting the International Health Regulations (2005) surveillance core capacity requirements at the subnational level in Europe: the added value of syndromic surveillance

BACKGROUND: The revised World Health Organization's International Health Regulations (2005) request a timely and all-hazard approach towards surveillance, especially at the subnational level. We discuss three questions of syndromic surveillance application in the European context for assessing public health emergencies of international concern: (i) can syndromic surveillance support countries, especially the subnational level, to meet the International Health Regulations (2005) core surveillance capacity requirements, (ii) are European syndromic surveillance systems comparable to enable cross-border surveillance, and (iii) at which administrative level should syndromic surveillance best be applied? DISCUSSION: Despite the ongoing criticism on the usefulness of syndromic surveillance which is related to its clinically nonspecific output, we demonstrate that it was a suitable supplement for timely assessment of the impact of three different public health emergencies affecting Europe. Subnational syndromic surveillance analysis in some cases proved to be of advantage for detecting an event earlier compared to national level analysis. However, in many cases, syndromic surveillance did not detect local events with only a small number of cases. The European Commission envisions comparability of surveillance output to enable cross-border surveillance. Evaluated against European infectious disease case definitions, syndromic surveillance can contribute to identify cases that might fulfil the clinical case definition but the approach is too unspecific to comply to complete clinical definitions. Syndromic surveillance results still seem feasible for comparable cross-border surveillance as similarly defined syndromes are analysed. We suggest a new model of implementing syndromic surveillance at the subnational level. In this model, syndromic surveillance systems are fine-tuned to their local context and integrated into the existing subnational surveillance and reporting structure. By enhancing population coverage, events covering several jurisdictions can be identified at higher levels. However, the setup of decentralised and locally adjusted syndromic surveillance systems is more complex compared to the setup of one national or local system. SUMMARY: We conclude that syndromic surveillance if implemented with large population coverage at the subnational level can help detect and assess the local and regional effect of different types of public health emergencies in a timely manner as required by the International Health Regulations (2005)

Désinclusion canine et thérapeutique bioprogressive

L'intérêt porté par les auteurs, qui se sont penchés sur la mise en place des canines incluses, témoigne de ce que régression de ces dents reste un problème mécanique et biologique complexe et délicat à résoudre : il n'est que de remarquer la facilité avec laquelle surviennent et persistent la récession gingivale péricervicale ou la sensation de tension douloureuse, dès qu'une force inadéquate en intensité et en direction leur est appliquée. Certains chercheurs tendent actuellement à penser que le clinicien devrait avoir recours à l'application de forces minima pour obtenir des effets optima, ces forces étant dépendantes de la surface de l'élément à déplacer. Dans cette optique, leur appréciation à l'aide d'une jauge devient imperative. Les principes d'action majeurs du ressort de désinclusion, développés dans ce travail, s'appuient sur cette notion

Le laquage fluoré : implications et applications orthodontiques

Plusieurs revues de synthèse récentes proposent l'établissement d'un maximum de mesures carioprophylactiques fluorées, adaptées tant à la spécialité orthodontique qu'à la spécificité du patient à traiter, dont la susceptibilité carieuse individuelle est prise en compte, au même titre que ses préférences, sa coopération, sa discipline et sa plus ou moins bonne compréhension 3, 4, 29, 33,. Les applications professionnelles de gels fluorés et l'utilisation personnelle de bains de bouche fluorés figurent au rang des meilleures techniques d'administration des fluorures : en ce sens, elles doivent constituer la base du système préventif dont dispose l'orthodontiste au cours de ses traitements. Par suite de leur grande efficacité, les vernis fluorés seront réservés, pour leur part, à la protection des zones rétentives juxtagingivales, à la reminéralisation des leucomes précarieux et à la restauration d'une minéralisation normale des dents incluses, mises en place sur l'arcade

Diagnostic téléradiographique sagittal des déformations verticales

Dans la première partie de ce travail, les auteurs rappellent les principales caractéristiques de toutes les analyses céphalométriques du sens vertical connues jusqu'alors, tout en essayant d'en faire la synthèse. Malgré leur abondance, il apparaît impossible de situer avec exactitude chaque élément du complexe cranio-facial dans le sens vertical, ce qui a conduit les auteurs à l'étude d'une méthode permettant d'atteindre cet objectif. Les malpositions alvéolaires peuvent être aisément dissociées des malpositions squelettiques, dans le sens vertical, car le principe de l'analyse repose sur des proportions de mesures prises sur le même tracé téléradiographique, et non pas sur des valeurs linéaires ou angulaires de référence. Cette analyse permet à l'orthodontiste de compléter son diagnostic clinique de manière plus précise, et le renseigne sur le site exact de la malformation dans le sens vertical, ainsi que son importance. Elle le conduit, de ce fait, à l'élaboration de plans de traitement mieux adaptés, et dont le double résultat esthétique et fonctionnel recherché se rapproche de la normalité