The Journal of experimental medicine
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In experimental anemia in dogs due to blood loss the term "available iron" as determined by the dipyridyl test has no physiological significance. Iron salts (100 per cent available by dipyridyl) given in optimum dose (560 mg. per 2 weeks) will cause a net production of 50 to 55 gm. hemoglobin above the control base line in anemic dogs. This means that an iron salt which is rated as 100 per cent available by the dipyridyl test is only 35 per cent physiologically available. ⋯ No investigator has reported any condition of copper deficiency in man or dog. In fact, in anemias copper is usually above normal concentration in the liver. It is unlikely, therefore, that in experimental anemia in dogs and in the various anemias of man, any significance attaches to the intake of copper.
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It will be well to restate the main problem at this point and to examine how far the accumulated data can help to elucidate it. The problem is this: Why are old mice generally resistant to all forms of peripheral inoculation of vesicular stomatitis virus when intracerebral injection is equally fatal for mice of all ages? The results of experiments in which the presence of virus was demonstrated by animal passage suggested that the reason can perhaps be found in (a) the different mechanisms of virus progression after intracerebral and peripheral injection, and (b) the development with age of localized barriers capable of halting the spread of virus (1, 2). The present study sought histological evidence for the nature of virus progression and for the changes observed in the older animals. ⋯ Tobacco mosaic virus has been found to produce different types of disease in certain plants of different ages; thus a widespread, systemic necrosis leads to the death of young Nicotiana rustica plants, while in old plants it is possible to produce necrotic foci in many parts of the plant by direct inoculation, although generalization does not occur from an isolated focus as it does in young specimens (19). In other words, age apparently does not change the whole plant, but it does transform something which allows the virus to spread easily from one site to another. MacNider (20) has observed that dogs which survive a severe type of hepatic injury from uranium, repair this injury with a special type of atypical, epithelial cell and become resistant not only to secondary intoxications by uranium but also by chloroform; he has also found that this change in epithelial cell type may be acquired as a product of senility, and that when it develops it imparts to the liver a degree of resistance to chloroform comparable to that induced by a process of repair following a severe hepatic injury from uranium nitrate.