. Tierische Schädlinge und Krankheiten. Medizinische Parasitologie ; Insekten als Überträger von Krankheiten. Lebensgeschichte von ASCARIS 275 im Darm weiter zu entwickeln, obwohl Tote in den Faeces gefunden. Nur etwa ein Prozent jemals erreichen die Lungen. Vom sechsten bis zum zehnten Tage die Larven gehen aus der Blutgefäße in die Lungenbläschen und Bronchien der Lunge und von dort über die Luftröhre in den Mund. Wenn die Pneumonie dpes nicht tödlich der Host erholt in 11 oder 12 Tage und nach dem 16. Tag frei von Parasiten ist. Die größte Larven beobachtet (Abb. 109 A) wurde in der Lunge eines gefunden

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. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. LIFE HISTORY OF ASCARIS 275 in the intestine to develop further, though dead ones are found in the faeces. Only about one per cent ever reach the lungs. From the sixth to the tenth days the larvae pass from the bloodvessels into the air sacs and bronchial tubes of the lungs and thence through the trachea to the mouth. If the pneumonia dpes not prove fatal the host recovers in 11 or 12 days and by the sixteenth day is free from parasites. The largest larva observed (Fig. 109A) was found in the lung of a rat on the tenth day after infec- tion; it measured 1.32 mm. „ m^i T^ i * i . < bia. 109. Developmental stages of (about tV of an inch) in length. AsmHs; a, freshly hatched larva; 6, larva The larvae cannot live in tap fyom lung ot rat on tenth day after infec- "^ tion. X 130. (Adapted from Stewart.) water but can survive 24 hours on damp bread and two days in a rat's lung. Capt. Stewart be- lieves that these experiments suggest that man is infected by food contaminated by larvae which have emigrated actively from the mouth of a rat while the rat was nibbling. Hogs were suc- cessfully infected by larval worms from the lungs of rats. That this is the usual life history of Ascaris must certainly be doubted. When it is remembered that a large per cent of chil- dren in all tropical countries are infected, and often very heavily infected, the improbability of more than a few at most of the infections arising in the manner indicated above is apparent. Of 5000 eggs ingested by a rat not more than 50 were recovered by Stewart from the lungs, and of these only very few could possibly be successful in reaching a human intestine by way of moist foods nibbled by rats within the preceding 24 hours. Moreover several very eminent parasitologists have been success- ful in producing infection by feeding ripe eggs to hogs and also to man. It seems much more probable that Capt. Stewart'

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• book
• bookcentury1900
• bookdecade1910
• bookpublishernewyorkjwiley