Page:Popular Science Monthly Volume 69.djvu/414

410 on rather to less familiar problems that are to-day puzzling the medical world.

Since 1860 various forms of Amœba have been found in the human intestine. In 1876 Loesch first claimed these rhizopods to be the cause of dysentery, and since that time students of the subject have been about equally divided into supporters of Loesch and his opponents. In recent times, however, the belief is widespread that two forms of the disease occur, one of which, tropical, pernicious, or amoebic dysentery, is invariably accompanied by the rhizopod Entamœba histolytica, which Schaudinn distinguishes from the ordinary harmless intestinal amœba A. coli. This form becomes a tissue and cell-infecting parasite and to this characteristic it owes its malignancy. Musgrave in the government laboratory at Manila has worked out the organism most carefully and has been successful in producing the disease in monkeys and other animals through cultures free from the ordinary forms of bacteria. The life history of the Amœba has been followed by Schaudinn, and in the present place this is perhaps more interesting than the pathological details.

The Amœba has little structural detail, a nucleated cell with minute form changes, a slight differentiation into ectoplasm and entoplasm, a great power of reproduction, by division and by budding, leading to masses of the organisms in the intestine and attached organs, where intestinal lesions, liver abscesses and the like, become the characteristic features of the disease. One interesting phenomenon worked out by Schaudinn is the preliminary nuclear metamorphosis before spore formation. In the majority of rhizopods in which the life history is known the formation of conjugating gametes is preceded by fragmentation of the nucleus either by division, or by a kind of nuclear secretion of chromatin. A condition of the cell, known as that of the 'distributed nucleus' results from this fragmentation and each fragment of chromatin becomes the nucleus of one of the gametes. Unfortunately, Schaudinn gives no figures in his preliminary publication on Entamœba, but his description tallies exactly with analogous processes in other rhizopods, notably in Arcella, Centropyxis, Difflugia and others.

In Entamœba as in these free-living rhizopods the spore-like bodies resulting from this distributed condition of the nucleus conjugate and so bring about a renewal of vitality of the parasite, favorable to the infection of new hosts. Musgrave has shown that these parasites may live a free life in ordinary drinking water and that infection takes place presumably in this way, and his observations indicate that Entamoeba is a facultative rather than an obligatory parasite of man.