Non-crystalline Forms Research Articles

TRANSFORMATIONS IN THE Feo/Fed RATIO OF PEDOGENIC IRON OXIDES AFFECTED BY IRON-REDUCING BACTERIA

In model experiments under controlled conditions of pH, particle size and amount of glucose, changes in the free Fe oxides (Fed) and acid oxalate soluble Fe (Feo) of six soils were studied after inoculation with iron-reducing, nitrogen-fixing Clostridia. In all soils, the total amount of Fed as well as crystalline Fe (Fed-Feo) decreased immediately and significantly, while Fe(II) in solution increased sigmoidally and was inversely proportional to changes in pH. Feo remained relatively constant throughout the incubation period. As a consequence, the Feo/Fed ratio increased in all samples. At the end of the reduction process, total dissolved Fe(II) correlated with the original Feo content and showed a negative correlation to Fed-Feo. These results are explained by a mechanism in which active non-crystalline iron oxides are reduced in preference to the crystalline forms. The latter are probably transformed and reduced to non-crystalline forms but not until all available active non-crystalline oxides have been exhausted. In the discussion, the reliability of acid oxalate-soluble Fe as a measure of the non-crystalline, active pedogenic iron forms is outlined. Further, the significance of a lowered redox potential (Eh or rH) in reductive transformations of flooded soils is analyzed.

Classification of non-crystalline solids

Considerable confusion is caused in the literature by lumping all non-crystalline solids under a single name, often “glass”. A solid of any composition may exist in several crystalline and also several non-crystalline forms, each having a different structure and set of properties. The existence of the differences between various non-crystalline forms has been neglected principally due to the lack of tools for structural analysis of aperiodic lattices. This paper proposes an interim classification of non-crystalline solids based on the method of preparation which gives rise to, and can be correlated with, the structural differences. The effectiveness of the scheme is illustrated for the case of the many genetically and structurally different non-crystalline forms of SiO 2.

Immunological factors in the pathogenesis of the hyaline tissue of silicosis.

Several hypotheses have been suggested in ex planation of the pathogenesis of silicosis. The earliest was the mechanical hypothesis, according to which, quartz particles, being pointed and sharp, would irritate the cells, stimulating their prolifera tion. This hypothesis was discarded when it was seen that other minerals, with edges even harder and sharper than quartz, such as carborundum and diamond, did not produce fibrosis. In 1922 Gye and Purdy put forward the chemical theory. They sug gested that silicic acid, on being slowly released by crystalline silica, would react as a toxic substance capable of inducing fibrosis. This hypothesis was long held, and until a short time ago it was sup ported and expanded by King (1947) and his colleagues. It was never clearly established how the dissolved silicic acid actually produced fibrosis. It was believed by some that monosilicic acid was the fibrogenic agent, and by others that it was poly merized silicic acid. However, no conclusive evidence has been produced to show that the dissolved silica induces fibrosis and by what means, and this is true also for the interesting hypothesis, recently put forward by Kikuth (1956), which focuses attention on the damage which monomeric silicic acid may exert on some cellular structures (mitochondria). In the last 10 years several physical hypotheses have been proposed: the piezoelectric (Velicogna, 1946; Evans, 1948) and radioactivity of quartz theories (Dantin-Gallego, 1948), both found un acceptable by Parmeggiani (1950), and also the most interesting and impressive hypothesis formulated by J?ger (1954) and Seifert (1954) in which they suggested that the crystalline lattice surface of the quartz would act as a matrix on which cellular proteins would reform and consequently be de natured. The reforming of the proteins would cause them to assume the shape and properties of fibrous proteins, hence the capacity of free crystalline silica for producing fibrous tissue. This theory is sup ported by the fact that amorphous silica is far less fibrogenic than crystalline silica (R?ttner, Willy, and Baumann, 1954). The arguments on the solubility hypothesis and on the hysical hypothesis of the action of surfaces led to numerous additional investigations. In an excellent critical paper, King, Zaidi, and Nagel schmi t (1956) summarized and discussed all the points for and against the theory of solubility. The facts which contradict the validity of this theory as originally stated are the discrepancy between the solubility of various forms of free silica and their fi rogenic action, and the improbability that there is polymerized silicic acid in the tissues. King himself arrived at the conclusion that the solubility of the silica could not serve itself to explain the patho genesis of silicosis. J?ger has ably illustrated the points in favour of the theory of surface action. However, he did not succeed in explaining why certain non-crystalline forms of silica, such as condensation silica (Policard and Co let, 1954), have some fibrogenic action. J?ger also has not explained why areas of massive fibrosis are formed, nor why other mineral dusts alon or in combination with a small percentage of quartz can, in certain conditions, cause massive fibrosis. It must be remembered that the hypotheses of chemical action and surface action were intended more to define the aetiological agent rather than the pathogenic mechanism of silicosis. They state that it is ither dissolved silicic acid or silica crystals as such which cause fibrosis; but how these factors actually induce the formation of this particular hyaline fibrous tissue of silicosis has never been satisfactorily explained. The theory of Holt and Osborne (1953) that polymerized silicic acid acts like mucopolysaccharides, facilitating and directing the formation of fibrils and hence the production of collagen, and the one proposed by J?ger that connective tissue formation would be induced directly by a fibrous transformation of proteins 8

Streptomycin in Tuberculosis

The immediate effects of crystalline streptomycin were studied in 44 patients with advanced pulmonary tuberculosis. The findings were evaluated in the light of results obtained in 31 patients treated with noncrystalline streptomycin, and in 11 patients treated with both forms. Viewed against a background of experience in the treatment of similar types of patients by conventional methods, it was found that: Crystalline streptomycin was associated with notable degrees of roentgenographic regression of the disease in approximately 60 per cent of patients with acute exudative, or recent caseocavernous tuberculosis. In a few it was associated with apparent arrest of the disease. The improvement was at a pace and to a degree seldom seen in similar types of patients treated on a rest regimen alone. In the remainder, the roentgenographic changes were rarely progressive under streptomycin treatment. They were either stationary or slightly regressive. Significant to marked symptomatic improvement occurred in the majority as evidenced in a decline of fever, decreased cough and expectoration, increased weight and improved well-being. Crystalline streptomycin was found to have no demonstrable effect on long-standing fibrocavernous tuberculosis. The potential toxic effects of streptomycin, particularly in older age groups, counterbalances any temporary improvement which may be derived from the use of the agent in this type of disease. Streptomycin was effective in the treatment of tuberculous laryngitis and bronchitis. Draining fistulas closed promptly, but occasionally reopened. It was of doubtful value in the treatment of chronic tuberculous empyemas, excepting possibly preoperatively. Streptomycin was found most valuable in conjunction with collapse and other surgical measures. In occasional instances it made surgical intervention unnecessary. Often it broadened the field of application of surgical treatment by rendering previously inoperable cases amenable to surgery. In the relatively small number of patients studied, no demonstrable differences could be detected in the immediate therapeutic effects in those treated with crystalline streptomycin as compared to those treated with the noncrystalline forms. It should be noted that the groups of patients in which the comparison was attempted were not treated simultaneously. Furthermore the patients treated with crystalline streptomycin had, by and large, more advanced tuberculosis often associated with serious complications. The toxic effects of crystalline streptomycin were, with few exceptions, not of a severity to cause abandonment of the treatment. Short interruptions were necessary in many instances. Crystalline streptomycin appeared to cause less pain at the site of injection and was less often associated with febrile reactions that the noncrystalline forms. However, stomatitis was more common with the former. Dizziness and allergic skin manifestations occurred with approximately the same frequency and intensity. The optimum daily and total dosages and the best manner of applying streptomycin were not established in this study.