Evolution of Knowledge Concerning the 
Roundworm Ascaris lumbricoides ' 
By BENJAMIN SCHWARTZ? 
Agricultural Research Service 
U.S. Department of Agriculture 
[With 2 plates] 
No HELMINTH is more familiar to laymen than the large intestinal 
roundworm that bears the name Ascaris lumbricoides. An intimate 
companion of man since time immemorial, and known to Hippocrates 
as the most conspicuous member of man’s intestinal worms, A. dum- 
bricoides was baptized in a zoological sense, along with its host Homo 
sapiens, in 1758—the date which marks the beginning of binomial 
zoological nomenclature. In recent years the long-sustained associa- 
tion between this nematode parasite and man has been considerably 
weakened, if not severed, wherever sanitary barriers have been inter- 
posed between the two. If the parasite has practically disappeared 
from its human host in urban and other well-sanitated areas, it 
still lives on a lavish scale in the populations of several continents, 
where millions of people are continuously exposed to its attacks at an 
apparently undiminishing rate. 
PREVALENCE OF ASCARIS 
Throughout the Middle Ages—probably also long before that 
time—and extending well into the 19th century, Ascaris was a wide- 
spread parasite of man practically throughout Europe. According 
to Stoll’s (25)% estimate of the extent of the current human helminthic 
infections throughout the world, Ascaris is of more common occur- 
rence than any of the other worms known to parasitize man. Stoll 
concluded that nearly 650 million human beings, about one-fourth of 
the estimated world’s population, serve as hosts to this helminth. 
Of those so affected, about 75 percent live in Asia. <A little less than 
one-third of the remaining 25 percent live in Europe, and about as 
1Theobald Smith Memorial Lecture given at a meeting of the New York Society of 
Tropical Medicine, May 21, 1959, in New York City. 
2 Retired December 1, 1959. 
3 Numbers in parentheses indicate references in the bibliography. 
465 
