Scanning electron microscopy study of bone intracortical vessels using an injection and fractured surfaces technique

The intracortical canal/vessel systems of long bones are not yet completely understood in terms of their morphology and physiology, mainly because of the difficulty of injecting the small calibre vessels and cutting the calcified matrix. Here, we apply a novel method combining perfusion of the vessels and fracture of the cortical bone to enlighten the architecture of this system. The femurs of ten rabbits were perfused with a water-soluble dye (China ink) or alcoholic glycerol solution, and the fractured cortex specimens were then examined by scanning electron microscopy (SEM). The results document: (1) the fibrillar structure of the canal surfaces; (2) the perivascular environment with cellular components in different phases of incorporation within the bone matrix; (3) previously unreported filamentous structures on the outer surface of vessels, which could be interpreted as non-myelinic nerve fibres; (4) the inner organisation of the cutting cones. Although based exclusively on morphology, these observation have some relevance to increasing knowledge of bone circulation physiology in the cortical bone

The Keynesian tutor. Kahn and the correspondence with Sraffa, Harrod and Kaldor

In this chapter, relying on new documentary evidence, the differences of approach, style and focus of those economists who were close to Keynes (Sraffa, Harrod, and Kaldor) are highlighted, in relation to Keynes’s ‘favourite pupil’ (as Kahn defined himself). Special importance is given to the period of the ‘Circus’, when Keynes’s new theories were arguing out (and sometimes independently developed) by the younger economists

Scanning electron microscopy study of bone intracortical vessels using an injection and fractured surfaces technique.

The intracortical canal/vessel systems of long bones are not yet completely understood in terms of their morphology and physiology, mainly because of the difficulty of injecting the small calibre vessels and cutting the calcified matrix. Here, we apply a novel method combining perfusion of the vessels and fracture of the cortical bone to enlighten the architecture of this system. The femurs of ten rabbits were perfused with a water-soluble dye (China ink) or alcoholic glycerol solution, and the fractured cortex specimens were then examined by scanning electron microscopy (SEM). The results document: (1) the fibrillar structure of the canal surfaces; (2) the perivascular environment with cellular components in different phases of incorporation within the bone matrix; (3) previously unreported filamentous structures on the outer surface of vessels, which could be interpreted as non-myelinic nerve fibres; (4) the inner organisation of the cutting cones. Although based exclusively on morphology, these observation have some relevance to increasing knowledge of bone circulation physiology in the cortical bone

Anatomy of the intracortical canal system. Scanning electron microscopy study in rabbit femur.

The current model of compact bone is that of a system of longitudinal (Haversian) canals connected by transverse (Volkmann’s) canals. Models based on histology or microcomputed tomography lack the morphologic detail and sense of temporal development provided by direct observation. Using direct scanning electron microscopy observation, we studied the bone surface and structure of the intracortical canal system in paired fractured surfaces in rabbit femurs, examining density of canal openings on periosteal and endosteal surfaces, internal network nodes and canal sizes, and collagen lining of the inner canal system. The blood supply of the diaphyseal compact bone entered the cortex through the canal openings on the endosteal and periosteal surfaces, with different morphologic features in the midshaft and distal shaft; their density was higher on endosteal than on periosteal surfaces in the midshaft but with no major differences among subregions. The circumference measurements along Haversian canals documented a steady reduction behind the head of the cutting cone but rather random variations as the distance from the head increased. These observations suggested discontinuous development and variable lamellar apposition rate of osteons in different segments of their trajectory. The frequent branching and types of network nodes suggested substantial osteonal plasticity and supported the model of a network organization. The collagen fibers of the canal wall were organized in intertwined, longitudinally oriented bundles with 0.1- to 0.5-lm holes connecting the canal lumen with the osteocyte canalicular system

Henri Gaudier-Brzeska (1891-1915): il genio interrotto

testo sull'opera di Henri Gaudier-Brzesk

The standard system and the tendency of the (maximum) rate of profit to fall - Marx and Sraffa: There and back

In notes written in the 1940s Sraffa rejected Bortkiewicz critique of Marx\u2019s theory of the tendency of the rate of profit to fall. First, he claimed that Marx\u2019s law was logically consistent and not flawed and that Bortkiewicz\u2019s criticism failed to grasp the essential meaning of Marx\u2019s theory, based on the determination of the maximum rate of profit in the economic system. However, Sraffa interpreted technical change that causes an increase in the organic composition of capital as a change that occurs given the technical knowledge available. The substitution of already-invented machinery for labour becomes profitable only when the wage rate increases. On the contrary, according to Sraffa, \u2018real\u2019 technological progress is generally neutral and does not involve an increase in the organic composition of capital. This interpretation is very interesting because it stresses the distinction between the analytical and logical aspects on the one hand, and the historical aspect of Marx\u2019s analysis on the other. Second, when writing his notes, Sraffa believed that even in the \u2018actual\u2019 economic system the relationship between aggregate income and aggregated capital does not change when the distribution of income varies. This assumption seems to play an important role in Sraffa\u2019s vindication of Marx\u2019s law. Thus the problem arises whether Sraffa\u2019s defence of the logical structure of Marx\u2019s law can be upheld even when this \u2018hypo\u2019 regarding the ratio between aggregate income and aggregate capital is dropped. In the following pages I will try to show that Sraffa\u2019s argument can be reformulated in terms of the Standard system and the Standard relationship between wage and profit rates. It will be shown that Sraffa himself maintained that the Standard system is a powerful tool in the interpretation of the Classical and Marxian theory of value. Moreover it is possible to compare two different Standard relationships because the quantities involved are comparable. In fact, they are the actual rates of profit and the maximum rate of profit