The making of a germ panic, then and now.

Over the last 2 decades, a heightened interest in germs has been evident in many aspects of American popular culture, including news coverage, advertisements, and entertainment media. Although clearly a response to the AIDS epidemic and other recent disease outbreaks, current obsessions with germs have some striking parallels with a similar period of intense anxiety about disease germs that occurred between 1900 and 1940. A comparison of these 2 periods of germ "panic" suggests some of the long-term cultural trends that contributed to their making. Both germ panics reflected anxieties about societal incorporation, associated with expanding markets, transportation networks, and mass immigration. They were also shaped by new trends in public health education, journalism, advertising, and entertainment media. In comparison to the first germ panic, the current discourse about the "revenge of the superbugs" is considerably more pessimistic because of increasing worries about the environment, suspicions of governmental authority, and distrust of expert knowledge. Yet, as popular anxieties about infectious disease have increased, public health scientists have been attracting favorable coverage in their role as "medical detectives" on the trail of the "killer germ."

Insertion of Tn916 into Bacillus pumilus plasmid pMGD302 and evidence for plasmid transfer by conjugation.

As part of an effort to develop systems for genetic analysis of strains of Bacillus pumilus which are being used as a microbial hay preservative, we introduced the conjugative Enterococcus faecalis transposon Tn916 into B. pumilus ATCC 1 and two naturally occurring hay isolates of B. pumilus. B. pumilus transconjugants resistant to tetracycline were detected at a frequency of approximately 6.5 x 10(-7) per recipient after filter mating with E. faecalis CG110. Southern hybridization confirmed the insertion of Tn916 into several different sites in the B. pumilus chromosome. Transfer of Tn916 also was observed between strains of B. pumilus in filter matings, and one donor strain transferred tetracycline resistance to recipients in broth matings at high frequency (up to 3.4 x 10(-5) per recipient). Transfer from this donor strain in broth matings was DNase-resistant and was not mediated by culture filtrates. Transconjugants from these broth matings contained derivatives of a cryptic plasmid (pMGD302, approx 60 kb) from the donor strain with Tn916 inserted at various sites. The plasmids containing Tn916 insertions transferred to a B. pumilus recipient strain at frequencies of approx 5 x 10(-6) per recipient. This evidence suggests that pMGD302 can transfer by a process resembling conjugation between strains of B. pumilus.

Use of a Plasmid DNA Probe To Monitor Populations of Bacillus pumilus Inoculant Strains in Hay.

We are evaluating naturally occurring isolates of Bacillus pumilus for use as microbial hay preservatives. Seven isolates of B. pumilus from hay contained a 42-kb cryptic plasmid (pMGD296). We wished to determine whether pMGD296 could be used as a molecular marker to follow populations of these isolates in hay over time. Southern blots and colony blots of 69 isolates of B. pumilus and other Bacillus spp. were probed with P-labeled pMGD296. Twenty-nine probe-positive isolates were identified; of these, 28 contained a plasmid with a restriction profile identical to that of pMGD296. One isolate from untreated hay contained a 40-kb plasmid (pMGD150) that was homologous to pMGD296 but had a different restriction fragment pattern. Regions of homology between the two plasmids were identified by Southern blotting, and a 1.9-kb HindIII-PstI fragment of pMGD296 lacking strong homology to pMGD150 was cloned in pUC18. The cloned fragment hybridized only with isolates containing pMGD296 and was used to estimate populations of these isolates in treated and untreated hay.

Human capital and the rise and fall of families.

"This paper develops a model of the transmission of earnings, assets, and consumption from parents to descendants. The model assumes utility-maximizing parents who are concerned about the welfare of their children. The degree of intergenerational mobility is determined by the interaction of this utility-maximizing behavior with investment and consumption opportunities in different generations and with different kinds of luck. We examine a number of empirical studies for different countries. Regression to the mean in earnings in rich countries appears to be rapid. Almost all the earnings advantages or disadvantages of ancestors are wiped out in three generations." A comment by Robert J. Willis is included (pp. 40-7).

Human capital and the time-profile of human fertility revisited.

PIP: This paper examines a model of the intertemporal distribution of births recently proposed by Cigno that concludes 1) the optimal time profile will satisfy the Hotelling rule of natural resources depletion, and 2) women with high initial endowments of human capital will have all their children early in married life while those with low initial endowments will spread childbearing more evenly over the fertile period. This paper argues that Cigno's model is inconsistent with the empirical evidence. Specifically, it is claimed that: 1) the natural resource analogy has been misapplied; 2) the stated 1st order conditions are incorrect; 3) optimal birth profiles do not satsify the Hotelling rule; and 4) the optimal time profile is for all women, regardless of their human capital, to concentrate births at the end of the fertile period. Since the discounted opportunity cost of a birth declines over time, it always pays to postpone a birth as long as possible. However, again, the theoretical prediction of delayed childbirth is not consistent with available evidence, suggesting that important factors have been omitted from this model.^ieng

Childlessness in Canada 1971: a further analysis.

PIP: This paper reexamines the correlates of childlessness in Canada, using a maximum likelihood probit estimation technique. Contrary to the conclusions of Grindstaff, Balakrishnan, and Ebanks, the author finds that selected ascribed attributes (religion and nativity) and achieved characteristics (labor force status, schooling, and/or family income) are significant correlates of childlessness, both for younger and older cohorts of women. Locational differences are also evident, particularly among older women (45 and over). Marriage duration is an important determinant of childlessness, especially among women who have been married relatively few years. Previous research is extended by analyzing the interaction between the labor force status and childlessness, taking into account self-selection in labor force participation. The determinants of childlessness differ between working and nonworking women, and husband's and wife's incomes operate in opposing directions.^ieng

Lifetime models of female labor supply, wage rates, and fertility.

PIP: A simple 1 period lifetime model is specified in which schooling is part of the lifetime period. This implies that an adding-up constraint is imposed on the uses of time in the lifetime including schooling, which may induce a negative correlation between years of schooling and years in the market, while producing a positive correlation between years of schooling and the fraction of the postschool lifetime spent in the market. The model is used to interpret empirical analyses based on alternative measures of lifetime labor supply and on alternative specifications of which variables may be treated as exogenous. In the empirical analysis the retrospective and longitudinal aspects of the newly available National Longitudinal Survey of Women is used to construct a measure of the fraction of the lifetime supplied to the market and measures of the lifetime wage rates of both the husband and the wife. The empirical results take the lifetime model of labor supply seriously in that the empirical measures of labor supply and wage rates bear a much closer resemblance to the theoretical concepts than measures typically employed in the literature. The estimates indicate that the "plausible assumptions" required for the true coefficient on fertility in a labor supply equation to be zero are fulfilled. These estimates are compared with those obtained using current measures as proxies for lifetime variables. Based on these estimates, an explanation is offered for the apparent contradiction between the findings of studies using a simultaneous equations approach that report no effect of fertility on female labor supply and the strong depressing effect of children on (current) labor supply obtained from research that treats children as exogenous. Current female hours appear more responsive to husbands' current earnings and female education than is the case with the lifetime variables. There are marked differences in the effects of race. The lifetime hours of white women are only some 2 1/2 years less than those of black women, whereas the current measure implies a difference of more than 8 years. Having a foreign nationality depresses the current measures by more than 5 years but has no significant effect over the lifetime. The crude proxy for nonlabor income, while only significant at the 10% level, depresses current labor supply more than it depresses the lifetime measure. Similarly, having a father with a college education reduces current labor supply but not lifetime hours. In the absence of a dynamic life cycle model nesting both the 1 period lifetime model and "current" period labor supply functions, it is not possible to provide a consistent explanation of the observed differences. Yet, the existence of these differences is sufficient to refute the notion that the lifetime quantities are distributed randomly across the "current periods."^ieng

Family labour supply and fertility: a two-regime model.

PIP: The central hypothesis of the "new micro-economics of fertility" was examined, i.e., because children are female-time intensive, fertility is inversely related to the mother's wage. A theoretical model of lifetime family labor supply and completed fertility which forms the basis for the subsequent empirical investigation is presented. Empirical estimates of the model are provided using 1971 Canadian census data. The 1-period model of completed family size and lifetime labor supply indicates that fertility and labor supply behavior of families where the wife participates in the labor market will differ from that of families with never-participating wives. The systematic differences arise because families with nonworking wives face the additional binding constraint of an inflexible supply of wife's time to the home. A comparison of these 2 regimes allows inferences concerning the female-time intensity of children and the substitutability of husband's and wife's time. In the context of the 1-period model, the relevant criterion for separating families into the 2 regimes is the lifetime rather than current participation status. The evidence suggests that when this procedure is followed, much doubt is cast on the conventional wisdom that children are female-time intensive. The usual inverse relation found between wife's wage or education and completed family size appears to be the result of a complex interaction between wage rates, lifetime labor force participation, and fertility. Some support is found for complementarity between the home time of the husband and wife, but the evidence is not totally consistent. Results of the female participation equation strongly suggest complementarity; proxies for the husband's lifetime labor supply suggest weak or zero complementarity. When the sample is split by current participation of the wife rather than lifetime participation, then the results support conventional wisdom concerning the female-time intensity of children and replicate Kneisner's finding of complementarity between husband and wife's time. Reconciling these differences within the framework of the 1-period model is difficult since it yields no predictions concerning current variables. Yet, since the wife's lifetime participation is the correct criterion for allocating families to the 2 regimes under the 1-period model, doubt must remain concerning the female-time intensity of children until the current lifetime results are reconciled.^ieng