. Animal parasites and human disease. Insect Vectors; Parasites; Parasitic Diseases; Medical parasitology; Insects as carriers of disease. 274 OTHER INTESTINAL ROUNDWORMS Ascaris lumbricoides, is now usually looked upon as a variety of the species which occurs in hogs in almost every country in the world, and which is sometimes known as A. suilla. The life history of Ascaris is usually thought to be very simple. The eggs, of which thousands are deposited by a single female, develop within the eggshell outside of the human body, in water, soil or manure piles, wherever the proper conditions of
. Animal parasites and human disease. Insect Vectors; Parasites; Parasitic Diseases; Medical parasitology; Insects as carriers of disease. 274 OTHER INTESTINAL ROUNDWORMS Ascaris lumbricoides, is now usually looked upon as a variety of the species which occurs in hogs in almost every country in the world, and which is sometimes known as A. suilla. The life history of Ascaris is usually thought to be very simple. The eggs, of which thousands are deposited by a single female, develop within the eggshell outside of the human body, in water, soil or manure piles, wherever the proper conditions of temperature can be found. The eggs (Fig. 108) are about mm. long by mm. wide (¥J<j by ^ of an inch), elliptical in form with a thick transparent shell, usually bile - stained, covered over outside by irregular albu- minous coats which give them a rough warty appearance. When passed from the diges- ts tive tract no sign of segmen- Fic 108. Egg of Ascaris; A, surface tation can be geen After view showing warty albuminous coat; B, same in "optical section," , with month or six weeks under favor- microscope focused on center of egg in- able conditionS in soil Or Water stead of on surface. the embryo will have devel- oped, and can then be seen rolled up within the shell. Even eggs which have been dried and exposed to the sun for months may contain active embryos. The egg may remain for months or years in this condition, resistant to both drying and freezing, until swallowed by a human being or other susceptible animal. In the dry condition the eggs may be blown about by the wind or carried on the feet of flies. The use of human faeces (night- soil) as a fertilizer undoubtedly results in wholesale contamina- tion of vegetables and other garden products. When swallowed by a suitable host the hard shell of the egg is dissolved off and the parasite is liberated in the small intestine. After about five or six weeks sexual maturity is reached, and the productio
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectparasites, bookyear19
