478 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
DISCUSSION 
From the foregoing account it is clear that the knowledge we have 
concerning A. lumbricoides has been accumulated slowly and patiently 
over a period perhaps as long as the history of man’s civilization. If 
little was added in 2,000 years or more to what was already known to 
Hippocrates about 400 B.C. or earlier, and to Aristotle several dec- 
ades later, it was because of the veil of superstition and ignorance 
that hung over men’s minds throughout the Middle Ages. The clouds 
that dimmed the spirit of inquiry into living phenomena were some- 
what lifted by the pioneering discoveries of Redi in the 17th century 
on the propagation of insects. It took almost two additional cen- 
turies, however, before medical and other biological investigators 
began to approach experimentally the problem of the mode and 
course of infection with this parasite. By this approach they grad- 
ually brought to light one fact after another, sometimes in rapid suc- 
cession, so that toward the middle of the 19th century, and during the 
ensuing two or three decades, much was discovered about how Ascaris 
spreads from one host to another. It remained for the researches 
that were carried out during the second, third, and fourth decades of 
this century to bring to light the unexpected mechanism of infection 
with a parasite that has been so intimately associated with man 
throughout the ages, and still is widespread practically the world over. 
In attempts to unravel the life cycle of Ascaris, a number of in- 
vestigators resorted to experimental inoculation of human beings, in- 
cluding children. Subjecting children to experimental inoculation 
with worms is a hazardous venture under any circumstances, and 
especially when Ascaris eggs constitute the inoculum. In the experi- 
ments carried out by Mosler and Lutz, pulmonary and other symp- 
toms were observed. Aside, however, from the potential danger 
involved in medical experiments with human beings, the practice of 
using children as test animals cannot under any circumstances be 
justified, even though the investigators who resorted to this practice 
believed, in the light of knowledge then available, that little, if any, 
risk was involved in inoculating youngsters with a helminth that so 
many of them would, sooner or later, acquire anyway. It should not 
be forgotten, however, that not all the investigators who helped to 
piece together the life cycle of this parasite used only others as test 
hosts. Leuckart, Grassi, Calandruccio, Yoshida, Koino, and other ex- 
perimenters did not hesitate to expose themselves to experimental in- 
fection with A. lumbricoides—an exposure that in the case of Koino, 
at any rate, was fraught with considerable danger to his health. 
The life history of Ascaris resembles a two-host system that ap- 
parently has become compressed into a single host. The possible 
biological significance of the early migratory cycle of the larvae, which 
