摘要:

Summary.The rate of development of the excitatory process in tissues may conveniently be characterised by a measure, the “Excitation Time,” which was formerly known as “Chronaxie.” This constant also measures roughly the rate of other processes in the tissue,e.g.action‐potential wave, conduction velocity, rate of contraction, etc. probably because all these processes are limited by the development of electrical states in the tissue.The excitation time of muscle (but not medullated nerve) is very largely dependent on the size of the electrodes used. This is easily explained in terms of a physical theory of excitation. If nerves are stimulated by the penetration of current through the nodes of Ranvier, these will constitute unvarying pore electrodes and account for the relative independence of nerve upon electrode size.According to Lapicque, paralysis by curare and other similar conditions is due to a great increase in chronaxie of the muscle, which initially was the same as that of the nerve. This standpoint, which is fundamental in Lapicque's school, is criticised in detail. In the first place, the evidence upon which the theory rests is inadequate, In the second, further work by Lapicque's school has rendered the theory so complicated that it is now of doubtful practical value. Lastly, the experiments of other workers appear to make the theory untenable.In the light of the rejection of Lapicque's views and of the dependence of excitation time upon the nature of the electrodes, it is necessary to review the significance of the measure, and to modify the technique of its determination. Some practical aspects are discussed, and it is pointed out that at present the chief application to biology is in the analysis of multiple excitabilities (e.g.muscle with nerve twigs, tonic and phasic muscles, etc.). But it must be emphasised that in this analysis it is essential to determine the whole strength‐duration curve if the results are to be

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1935.tb00474.x

出版商:Blackwell Publishing Ltd    

年代:1935

数据来源: WILEY

摘要:

Zusammenfassung.1. Viele Organismen folgen in ihren Lebensgewohnheiten kosmischen Periodi‐zitaten. So haben sich z. B. manche Meeresorganismen dem regelmässigen Wechsel der Gezeiten angepasst, indem sie während bestimmter Stunden Schutzreaktionen ausfähren. Viele Vögel folgen in ihrem Verhalten dem Wechsel der Jahreszeiten. Das bekannteste Beispiel für den Einfluss kosmischer Rhythmen ist die unter den Lebewesen weit verbreitete Anlehnung an den periodischen Lichtwechsel; es ist dies der dem Wechsel von Tag und Nacht angepasste Wechsel von Ruhe und Aktivität.Diese “Biologischen Rhythmen” treten vielfach auch dann noch einige Zeit selbständig in Erscheinung, wenn durch konstante Bedingungen in einem Versuchsraum die direkten Einflüsse der kosmischen Periodizitäten ausgeschaltet werden. Ihr Ablauf fällt in vielen Fällen—trotz Wegfalles des gewohnten periodi‐schen Reizes—noch “pünktlich” mit dem zeitlichen Ablauf der Aussenfaktoren zusammen. Dieses Zeitgedächtnis ist nicht variabel, sondern streng gebunden an den “eingelernten” Rhythmus. Ob es seine Entstehung einer erblich oder individuell erworbenen “Erinnerung” verdankt, ist noch unbekannt.2. Eine höhere Stufe stellt das Zeitgedächtnis einiger sozialer Insekten (Bienen, Ameisen, Termiten) dar. Hier ist der Organismus nach voraus gegangener “Dressur” imstande, im Rahmen des 24‐stündigen Tages jede beliebige Stunde zu bestimmen. Wir haben hier also ein variables Zeitgedächtnis, das, wie nachgewiesen, von äusseren Periodizitäten ganz unabhängig ist. Das Zeitgedachtnis der genannten Insekten ist zahlreichen Untersuchungen unterzogen worden, welche das ganze Problem entscheidend gefordert haben. So wissen wir heute, dass die “Uhr,” die dieses verblüffend präzise Zeitgedächtnis bestimmt und entscheidend beeinflusst, die Geschwindigkeit des Stoffumsatzes im Körper ist. Es wird angenommen, dass diesem ausgesprochenen Zeitgedächtnis eine biologische Bedeutung im Zusammenhang mit dem Nahrungserwerb dieser sozialen Insekten zugrunde liegt. Eine entsprechende Fähigkeit ist uns bisher bei keiner anderen Tiergruppe in diesem Ausmasse bekannt.3. Die dritte Stufe des Zeitgedächtnisses ist die Fähigkeit, bestimmte Zeitstrecken frei nach ihrem Ablauf zu schätzen, wenn sie nicht im Rahmen einer regelmässigen Wiederholung und Reihenfolge als “Dressur” geboten werden. Derartige Versuche wurden bisher nur mit der weissen Ratte und dem Menschen angestellt. Bei beiden konnte die Fähigkeit zum Abschätzen kurzer Zeitspannen bis zu einem gewissen Grade nachgewiesen werden.Summary.1. The habits of many living organisms are subject to cosmic periodicities. A number of marine animals, for example, are adapted to the ebb and flow of the tides, and many birds follow the changes of the seasons in their behaviour. The most familiar example of the influence of cosmic rhythms is the widespread dependence of living organisms on periodic light changes; their alternations of rest and activity correspond with night and day.These biological rhythms frequently continue after the direct influence of cosmic periodicities has been experimentally removed. In spite of the absence of the usual periodic stimulus, the course of a biological rhythm may correspond punctually with the time sequence of the external factors. It is unknown whether such rhythms are due to inherited “memory” or are individually acquired.2. The time memory of certain social insects (bees, ants, termites) is on a higher level. These animals, after “training,” are capable of determining any hour of the day and their time memory is independent of external periodicities. The “clock” which here determines the hour with such remarkable precision has been shown to be the rate of metabolism in the body. It is assumed that this time memory has a meaning in connection with the acquisition of food by these insects. No corresponding time memory is known in any other group of animals.3. The third level of time memory is the capacity of estimating periods of time, without the latter having been impressed on the animal by “training.” Experiments to test this faculty have up to the present been performed only with white rats and with man. In both cases

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1935.tb00475.x

出版商:Blackwell Publishing Ltd    

年代:1935

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1935.tb00476.x

出版商:Blackwell Publishing Ltd    

年代:1935

数据来源: WILEY

摘要:

Summary.The present status of our knowledge of the form and structure of the plant body in the genusUtricularia(incl.BiovulariaandPofypompholyx), apart from the formal morphological point of view, is briefly presented.The account embraces (a) the period of embryological development, during which anatomical‐nutritional relations are prominent; a very peculiar feature is the abstriction of the root pole of the embryo by the endosperm; (b) the form of the rootless definitive embryo; and (c) its behaviour during germination, of which there are several types.Then follow descriptions of the various biological forms of the so‐called leaf, stolon, tubers and resting buds.The various forms of the trap (bladder) are described. While all have the same fundamental structure, the general form may be extremely simple in bearing no appendages, or may be equally complex in having numerous appendages of various kinds. The biological meaning of these is problematical.The entrance mechanism of the trap is analysed and its mode of operation is shown. It is composed of two valves, the larger being the door, and the smaller being the velum, which overlies the edge of the larger. When the trap is set the door edge rests against an opposing surface of a ridge, the threshold, which impedes its swinging inwards, and in this position the door and the velum are mutually so adjusted as to be watertight. The setting of the trap is achieved by diffusion of water from its interior, a condition of unstable equilibrium being set up. The adjustment of the trap to this condition consists in the partial collapse of its side walls. Springing of the trap consists in disturbance of some sort of release mechanism consisting of bristles, larger or shorter trichomes, which thus distort the door, allowing the higher outer water pressure to swing it in. The entering water current carries in the prey if suitably placed.Although ali the traps known are alike in principle of action, there is a considerable diversity of form and structure. The differences lie in the relative positions of the threshold and valves, and in the relative quantitative importance of their mutual thrusts. Such differences are expressed in an extended variety of form of every p

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1935.tb00477.x

出版商:Blackwell Publishing Ltd    

年代:1935

数据来源: WILEY

摘要:

Summary.Comparisons of the Protozoa and Metazoa have emphasised their structure‐function relationships without due regard to their historical relationships. Thus cellularity has been a common basis for this comparison as applied to unicellular organisms on the one hand and multicellular organisms on the other, equating in each group the cell as the unit of structure and function; or, on the contrary, denying that this comparison holds since Protozoa are to be regarded as non‐cellular organisms.It is proposed that genetic history, including both ontogeny and phylogeny, is the essential basis for this comparison. Since organic differentiation is the process by which the cell originated in phylogeny and each organism develops in ontogeny, maintaining its organismal unity throughout, it is suggested that primarily this process, protoplasmic differentiation, and secondarily its product, the primordial cell, should be given first importance in fundamental considerations of both protozoan and metazoan genetic history.Protozoa as well as Metazoa begin their life cycle as a primordial cell which is the stage of minimal protoplasmic differentiation. From this primordial stage comes to be differentiated epigenetically diverse organs with specific functions, derived for the Metazoa during numberless mitotic divisions but for the Protozoa during one mitotic division and are rederived during each succeeding division. Thus, Protozoa retain the capacity to reorganise, that is, to dedifferentiate and redifferen‐tiate, which they tend to do during fission, conjugation, endomixis, cystment, and regeneration; and are accordingly potentially immortal. Metazoan ontogeny, however, proceeds toward a fixed and irreversible state of differentiation which eventuates in disintegration and death.It is postulated further that protoplasmic reorganisation involves both cytoplasmic and nuclear structures which alike undergo a redifferentiation following dedifferentiation toward a primordial stage which represents the initial stage of the life cycle. While these changes may differ, with respect to the cytoplasm and nucleus, in the time, manner, or completeness of their occurrence; it is suggested that their visible manifestations have to do with dynamic processes which are fundamentally the

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1935.tb00478.x

出版商:Blackwell Publishing Ltd    

年代:1935

数据来源: WILEY