THE KINETICS OF SENESCENCE

The course of decline of vitality with age due to the process of senescence, when not complicated by the process of growth, follows a simple exponential law; that is the degree of vitality or of senescence (defining vitality as the reciprocal of senescence) at any moment is, regardless of age, a constant percentage of the degree of vitality or senescence of the preceding moment. This exponential law is the same as the law of monomolecular change in chemistry. During the actively growing period of life the index of vitality rises, due to the process of growth and the course of vitality in the case when the growing period is included in the vitality curve, follows a rising and falling course. This rising and falling course may often be represented by an equation containing two exponential terms which is practically the equation used to represent the course of accumulation and disappearance of a substance as the result of two simultaneous consecutive monomolecular chemical reactions.     

THE RATE OF GROWTH OF THE DAIRY COW : V. EXTRAUTERINE GROWTH IN LINEAR DIMENSIONS.

Barring fluctuations due to the cyclic phenomena, the extrauterine course of growth in linear dimensions and in weight of the dairy cow follows an exponential law having the same form as the law representing the course of monomolecular change in chemistry. This suggests the interpretation that the general course of growth is limited by a monomolecular chemical process, and that the cyclic phenomena are due to subsidiary processes in the fundamentally exponential course of growth. The fact that growth follows or tends to follow an exponential course may be stated more simply as follows: if the unit of time is taken sufficiently large so that fluctuations due to the cyclic phenomena are balanced or eliminated, then the amount of growth made during the given unit of time at any age tends to be a constant percentage of the growth made during the preceding unit of time. Thus, the growth in height at withers made during any year is about 34 per cent of the growth made during the preceding year. Similarly the growth in weight made during any year is about 56 per cent of the growth in weight made during the preceding year. This is in accordance with expectations if it is assumed that each animal begins life with a definite endowment of limiting substance necessary for the process of growth, and that this endowment is used up at a constant rate (or percentage) of itself.     

THE RATE OF GROWTH OF THE DAIRY COW : IV. GROWTH AND SENESCENCE AS MEASURED BY THE RISE AND FALL OF MILK SECRETION WITH AGE.

Data are presented on the effect of age on milk secretion in the dairy cow. From the age when milk secretion usually begins (2 years) to the age when maximum body weight is reached (about 8 years) increase of milk secretion and increase of body weight with age follow the same exponential course, which is the course of a monomolecular reaction of chemistry. After this age, unlike body weight which remains practically constant, milk secretion declines exponentially, that is, the course of decline follows the course of decline of a monomolecular reaction. The whole course of milk secretion with age was therefore found to follow approximately the course of two simultaneous, consecutive, monomolecular reactions. This is taken to mean that growth and senescence go on simultaneously from the beginning to the end of life, and that each follows an exponential law with age; and therefore perhaps that the course of the two processes are limited by two consecutive chemical reactions.     

THE EFFECT OF GESTATION ON THE RATE OF DECLINE OF MILK SECRETION WITH THE ADVANCE OF THE PERIOD OF LACTATION

1. Data are presented showing that the course of decline of milk secretion with the advance of the period of lactation in farrow cows follows the course of decline of a monomolecular chemical reaction, that is each month''s milk production is a constant percentage of the production of the preceding month (94.77 per cent in the case of the cow under consideration), from which it is inferred that milk secretion is limited by a chemical reaction initiated at parturition, and declining with the decrease of the concentration of the limiting substance as it is transformed into milk. 2. Data are presented showing that the decline in milk secretion due to pregnancy is related to the increase in weight of gestating animals, from which it is inferred that growth of the fetus is in part, at least, responsible for the decline in the milk flow due to the demand of the fetus for nutrients to support its life processes.     

OPTIMALITY THEORY,GOMPERTZ' LAW,AND THE DISPOSABLE SOMA THEORY OF SENESCENCE

The “disposable soma” theory for the evolution of senescence suggests that senescence arises from an optimal balancing of resources between reproduction and somatic repair. Dynamic programming models are constructed and analyzed to determine the optimal relationship between reproduction, diversion of resources from repair, and added senescent mortality. Of particular interest is the relationship between the repair-reproduction trade-off and the form of the mortality-rate-versus-age curve predicted. The models analyzed in the greatest detail assume that the relationship between reproduction and added senescent mortality does not change with age. These suggest that mortality should increase at an increasing rate with age, but may approach a linear rate as mortality becomes very high. General results are derived for the shape of the mortality curves early and late in the senescing part of the life span, and mortality curves for specific trade-off functions are illustrated. An exponential increase in death rate with age (Gompertz' Law) corresponds to only one of many possible relationships between reproduction and aging. The “Law” is unlikely to hold generally if the disposable soma theory accounts for a large fraction of the observed senescent increase in mortality with age. However, support for the generality of Gompertz' Law is weak, and other theories have not produced an evolutionary explanation for the law. The disposable soma theory is consistent with some of the exceptions to Gompertz' Law that have been observed.     

Statistical Basis for Predicting Technological Progress

Forecasting technological progress is of great interest to engineers, policy makers, and private investors. Several models have been proposed for predicting technological improvement, but how well do these models perform? An early hypothesis made by Theodore Wright in 1936 is that cost decreases as a power law of cumulative production. An alternative hypothesis is Moore''s law, which can be generalized to say that technologies improve exponentially with time. Other alternatives were proposed by Goddard, Sinclair et al., and Nordhaus. These hypotheses have not previously been rigorously tested. Using a new database on the cost and production of 62 different technologies, which is the most expansive of its kind, we test the ability of six different postulated laws to predict future costs. Our approach involves hindcasting and developing a statistical model to rank the performance of the postulated laws. Wright''s law produces the best forecasts, but Moore''s law is not far behind. We discover a previously unobserved regularity that production tends to increase exponentially. A combination of an exponential decrease in cost and an exponential increase in production would make Moore''s law and Wright''s law indistinguishable, as originally pointed out by Sahal. We show for the first time that these regularities are observed in data to such a degree that the performance of these two laws is nearly the same. Our results show that technological progress is forecastable, with the square root of the logarithmic error growing linearly with the forecasting horizon at a typical rate of 2.5% per year. These results have implications for theories of technological change, and assessments of candidate technologies and policies for climate change mitigation.     

THE COLLOIDAL BEHAVIOR OF EDESTIN

1. It has been shown by titration experiments that the globulin edestin behaves like an amphoteric electrolyte, reacting stoichiometrically with acids and bases. 2. The potential difference developed between a solution of edestin chloride or acetate separated by a collodion membrane from an acid solution free from protein was found to be influenced by salt concentration and hydrogen ion concentration in the way predicted by Donnan''s theory of membrane equilibrium. 3. The osmotic pressure of such edestin-acid salt solutions was found to be influenced by salt concentration and by hydrogen ion concentration in the same way as is the potential difference. 4. The colloidal behavior of edestin is thus completely analogous to that observed by Loeb with gelatin, casein, and egg albumin, and may be explained by Loeb''s theory of colloidal behavior, which is based on the idea that proteins react stoichiometrically as amphoteric electrolytes and on Donnan''s theory of membrane equilibrium.     

ULTRASTRUCTURAL OBSERVATIONS ON THE DISCHARGE OF TWO KINDS OF GRANULES IN THE FERTILIZED EGGS OF CYPRINUS CARPIO AND CARASSIUS AURATUS

This paper describes mainly ultrastructural evidence on the discharge of two kinds of granules, CA and CB, as well as the cortical alveoli in an egg of the common carp and the goldfish. The cortical alveoli (about 2–28 μ in diameter) and CA-granules (about 0.4–2 μ in diameter) are located in the cortical cytoplasm of the mature egg, and the latter is distinguishable in size and texture from the former which contains an eccentric core at the very least as a basal internal structure. The CB-granules (about 100–950 mμ in diameter) appear in small or large clusters in the cortical cytoplasm after fertilization, being formed in connection with constriction or pinching-off of dilated tubular elements. After fertilization the cortical alveoli, CA- and CB-granules are discharged at different times. The new plasmalemma of a fertilized egg appears to be a joint production of the original plasmalemma and the limiting membranes of the cortical alveoli, CA- and CB-granules.     

ON THE THEORY OF NERVOUS CONDUCTION

Assuming that the propagation of the nervous impulse consists in the excitation of adjacent regions of the nerve by the action current of the already excited region, exact equations for the velocity of such a propagation are established and integrated. The result depends on the assumptions which we make about the laws of excitation. If Hoorweg''s law is accepted, it is found that the velocity of propagation decreases exponentially with time, and that there is a limiting distance which the impulse will travel and which cannot be exceeded. If however a set of equations proposed by L. Lapique is assumed to govern the process of excitation, we find that the velocity of propagation asymptotically reaches a constant value.     

Interaction Mortality: Senescence May Have Evolved because It Increases Lifespan

Given an extrinsic challenge, an organism may die or not depending on how the threat interacts with the organism''s physiological state. To date, such interaction mortality has been only a minor factor in theoretical modeling of senescence. We describe a model of interaction mortality that does not involve specific functions, making only modest assumptions. Our model distinguishes explicitly between the physiological state of an organism and potential extrinsic, age-independent threats. The resulting mortality may change with age, depending on whether the organism''s state changes with age. We find that depending on the physiological constraints, any outcome, be it ‘no senescence’ or ‘high rate of senescence’, can be found in any environment; that the highest optimal rate of senescence emerges for an intermediate physiological constraint, i.e. intermediate strength of trade-off; and that the optimal rate of senescence as a function of the environment is driven by the way the environment changes the effect of the organism''s state on mortality. We conclude that knowledge about the environment, physiology and their interaction is necessary before reasonable predictions about the evolution of senescence can be made.     

AGE DEPENDENCE OF THE NUMBER OF THE STEM CELLS IN HAEMOPOIETIC TISSUES OF RATS

The number and concentration of haemopoietic stem cells in the femoral bone marrow and spleen of Wistar rats of different ages were investigated. Stem cells were assayed by the spleen colony technique in irradiated rat recipients. The ability of the recipient spleen to harvest transplanted tissue as a macroscopic colony was found to be dependent on the recipient's age. Changes with senescence were observed also in the concentration and the size of the stem cell compartment both in the marrow and spleen. No differences were demonstrated in the seeding of transplanted colony-forming units into the spleen of recipients of 1 and 4 months of age. A rats-mice strain difference in the effect of senescence on the haemopoietic stem cells is discussed.     

THE DARK ADAPTATION OF THE EYE OF THE HONEY BEE

Bees which are held in a fixed position so that only head movements can be made, respond to a moving stripe system in their visual field by a characteristic motion of the antennae. This reflex can be used to measure the bee''s state of photic adaptation. A curve describing the course of dark adaptation is obtained, which shows that the sensitivity of the light adapted bee''s eye increases rapidly during the first few minutes in darkness, then more slowly until it reaches a maximum level after 25 to 30 minutes. The total increase in sensitivity is about 1000 fold. The adaptive range of the human eye is about 10 times greater than for the bee''s eye. The range covered by the bee''s eye corresponds closely to the adapting range which is covered by the rods of the human eye.     

An Alternative Method for Evaluating Soybean Tolerance to Heterodera glycines in Field Plots

Alternate planting dates and periodic destruction of the previous year''s soybean crop as well as 1-year bare fallow were used to establish a range of population densities ofHeterodera glycines for the subsequent year. Soybean cultivar Coker 156 (susceptible, moderately tolerant) was compared to cultivars Essex (susceptible, intolerant) and Bedford (resistant) to evaluate tolerance at different H. glycines population densities established through the previous year''s treatments. Yield of Coker 156 was consistently intermediate between yields of Bedford and Essex in 1986 and 1987. Yield of Essex was negatively correlated (P = 0.05) with preplant egg numbers of H. glycines in 1987, whereas yield of Bedford and Coker 156 were not related to nematode density. Reproduction of H. glycines was greater (P = 0.05) on the moderately tolerant Coker 156 than on either of the other cultivars.     

海南文昌鸡若干种质特征和遗传多样性研究

对产于热带亚热带的文昌鸡若干种质特性进行了测定,采用RAPD技术分析其遗传多样性,并与其它生态类型鸡种进行了比较研究．结果表明,文昌母鸡羽毛以棕褐色、黄褐色和黄麻色为主,占群体80．83％;公鸡以红色、背翼部夹杂黑羽为主,占群体71．96％．文昌鸡的胚色大多为黄色．文昌鸡的生长速度比其它生态类型鸡种较慢,40周龄公母鸡的体重、体斜长和胚长也较小,明显具有热带亚热带生态特征．文昌鸡性早熟,母鸡127d产蛋率5％,182d产蛋率50％,300d产蛋量73个,平均蛋重37．6±3．2g．对文昌鸡基因组DNA进行RAPD分析,鸡群个体或群体间平均相似系数为0．6071-0．9699,表明文昌鸡的同源性普通高于内地其它鸡种,保持了品种的纯度．     

Ageing in a variable habitat: environmental stress affects senescence in parasite resistance in St Kilda Soay sheep

Despite widespread empirical evidence for a general deterioration in the majority of traits with advancing age, it is unclear whether the progress of senescence is chronologically determined, or whether factors such as environmental conditions experienced over the lifespan are more important. We explored the relative importance of ‘chronological’ and ‘environmental’ measures of age to changes in parasite resistance across the lifespan of free-living Soay sheep. Our results show that individuals experience an increase in parasite burden, as indicated by gastrointestinal helminth faecal egg count (FEC) with chronological age. However, chronological age fails to fully explain changes in FEC because a measure of environmental age, cumulative environmental stress, predicts an additional increase in FEC once chronological age has been accounted for. Additionally, we show that in females age-specific changes are dependent upon the environmental conditions experienced across individuals'' life histories: increases in FEC with age were greatest among individuals that had experienced the highest degree of stress. Our results illustrate that chronological age alone may not always correspond to biological age, particularly in variable environments. In these circumstances, measures of age that capture the cumulative stresses experienced by an individual may be useful for understanding the process of senescence.     

ON THE QUANTITY OF ELECTRICITY AND THE ENERGY IN ELECTRICAL STIMULATION

Weiss''s and Hoorweg''s laws are discussed with respect to the dynamics of the excitatory process. The former is shown to have a simple basis which is inadequate, however, because it implies a constant rate of subsidence of the state of excitation. Hoorweg''s law does not follow logically from the same basis so the two laws do not represent the same excitatory mechanism. Experimental data do not give minimal energies at 2 rheobases as predicted by each law. The experimental minima with direct currents are at 1.5 or more rheobases, while with condenser stimuli they are from 2.5 to 3.0 rheobases. These minima conform to the predictions of the writer''s equations which give the direct current minima as variable with a lower limit at 1.5 rheobases and the condenser minima as constant at e = 2.718 rheobases. The reasons for these differences are discussed and it is concluded that considerations of the quantity of electricity and the energy, per se, do not lead to any simple concepts with regard to the excitatory mechanism. The existing quantity and energy relations are, however, easily correlated in terms of the dynamics of the excitatory mechanism.     

ANALYSIS OF THE PROLIFERATION KINETICS OF BURKITT'S LYMPHOMA CELLS

The in vitro proliferation kinetics of a cell line derived from a patient with American Burkitt's lymphoma were investigated at three different growth phases: lag (day 1), exponential (day 3) and plateau (day 5). The growth curve, labeling and mitotic indices, percentage labeled mitosis (PLM) curves and DNA content distributions were determined. The data obtained have been analysed by the previously developed discrete-time kinetic (DTK) model by which a time course of DNA distributions during a 10-day growth period was characterized in terms of other cell kinetic parameters. The mean cell cycle times, initially estimated from PLM curves on days 1, 3 and 5, were further analysed by the DTK model of DNA distributions and subsequently the mean cell cycle times with respect to DNA distributions during the entire growth period were determined. The doubling times were 39·6, 31·2 and 67·2 hr, respectively, at days 1, 3 and 5. The mean cell cycle time increased from 23·0 to 37·7 hr from day 3 to day 5 mainly due to an elongation of the G₁ and G₂ phases. A slight increase in the cell loss rate from 0·0077 to 0·0081 fraction/hr was accompanied by a decrease in the cell production rate from 0·0299 to 0·0184 fraction/hr. This calculated cell loss rate correlated significantly with the number of dead cells determined by trypan blue exclusion. Analysis of the number of dead cells in relation to the cell cycle stage revealed that a majority of cell death occurred in G₁ (r= 0·908; P < 0·0001). There was a good correlation between the in vitro proliferation kinetics at plateau phase of this Burkitt's lymphoma derived cell line and the in vivo proliferation kinetics of African Burkitt's lymphoma (Iversen et al., 1974), suggesting the potential utility of information obtained by in vitro kinetic studies.     

贡嘎山峨眉冷杉林凋落物的特征

 研究了贡嘎山峨眉冷杉（Abies fabri）林凋落物量、凋落物特征及其N、P、K、有机碳的归还量,并探讨了它们在演替进程中的变化。结果表明,峨眉冷杉成熟林、中龄林和幼龄林的凋落物量依次为：2 809.925、2 787.086、2 043.585 kg·hm-2·a-1;其中N、P、K的归还量依次为：34.850、33.917、42.571 kg·hm-2· a-1。峨眉冷杉林凋落物量及其N、P、K的归还量较少,与我国其它森林区针叶林存在一定差异,而与美国西北部冷杉林相近。     

A NOTE ON THE SIMILARITIES BETWEEN THE CURVES OF GROWTH AND OF REGENERATION

The curves of growth and of regeneration follow the same course, and can be represented by the same exponential equation. This is taken to substantiate the theory that growth and regeneration are essentially identical processes governed by the same laws. A common peculiarity of the curves of growth and of regeneration is that during a short period in the early stages of regeneration and of growth, the apparent observed speed of these processes seems to be relatively slow. As a result, the curve of the fitted equation cuts the time axis not at zero, the beginning of growth or regeneration, but somewhat later. Data on regeneration are cited indicating that the initial slow phase of regeneration is due to the time required for the formation of a cap of embryonic cells which serves as a basis for the more active later regeneration; in other words, to qualitative growth which cannot be expressed in terms of quantitative units. It is suggested that the apparent initial slow phase of growth of the individual from the fertilized egg is due to a similar qualitative growth. It is suggested that if the initial qualitative changes could be converted into some common unit with the subsequent quantitative changes, the apparent initial lag would disappear, and the exponential equation representing the course of these processes would then be the same as the equation used to represent the course of a monomolecular chemical reaction. Certain implications of this reasoning are discussed in the text.     

BRIGHTNESS DISCRIMINATION AS A FUNCTION OF THE DURATION OF THE INCREMENT IN INTENSITY

1. This investigation has been concerned with an analysis of brightness discrimination as it is influenced by the duration of ΔI. The durations used extend from 0.002 second to 0.5 second. 2. ΔI/I values at constant intensity are highest for the shortest duration and decrease with an increase in duration up to the limits of a critical exposure time. At durations longer than the critical duration the ratio ΔI/I remains constant. 3. The Bunsen-Roscoe law holds for the photolysis due to ΔI. This is shown by the fact that, within the limits of a critical duration, the product of ΔI and exposure time is constant for any value of prevailing intensity, I. 4. At durations greater than the critical duration the Bunsen-Roscoe law is superseded by the relation ΔI = Constant. This change of relation is considered in the light of Hartline''s discussion (1934). 5. The critical duration is a function of intensity. As intensity increases the critical duration decreases. 6. Hecht''s theory (1935) accounts for the data of this experiment if it be assumed that brightness discrimination is determined by a constant amount of photolysis.