468 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
least in some quarters in France, as late as 1853. He quotes from a 
then current article the following view on the origin of ascarids: 
In the predisposition to worms, the thick mucus of the intestine comes under 
our consideration in the first place, as, being acid itself, it cannot purify the 
blood from acids. From a portion of the mucus the worms are produced by 
generatio aequivoca, with the assistance of asthenia and adynamia. The worms 
produced, as the analysis shows, are still more acid than the mucus, from 
which they are produced. Emetics, drastic purgatives, mercury, antimony, and 
arsenic, certainly kill the worms, but weaken the constitution, and thus actually 
rouse the generatio aequivoca into activity, and thus actually cause the forma- 
tion of worms. 
This was perhaps the last stand to uphold the thesis of the spon- 
taneous generation within the body of intestinal helminths—a view 
that had already crumbled for the most part before the scientific 
onslaught initiated by Redi almost two centuries earlier. It was 
Redi who discovered sex and eggs in Ascaris and made observations 
on the reproductive organs of this worm. 
RESISTANCE OF ASCARIS EGGS 
The remarkable adaptability of Ascaris to external conditions of all 
kinds is due in a large measure to the “toughness” of its eggs—the 
connecting link between the generations of worms. So great, in fact, 
is the impermeability of the egg shells, that “their development is 
not arrested in spirits of wine, chromic acid, or oil of turpentine” 
according to Heller (9) who investigated the embryonation of the 
cat ascarid nearly a century ago. In the laboratory Ascaris eggs 
are routinely cultured in a 2-percent solution of formalin, or in solu- 
tions of potassium bichromate, and they are said to have been cultured 
successfully in solutions of hydrochloric, sulfuric, nitric, and acetic 
acids, in strengths up to 50 percent, and in other solutions known 
to be highly deleterious to living matter. 
Parallel to the resistance of the eggs to inimical environmental 
influence is the long persistence of the embryos within the egg shells. 
A number of investigators have reported eggs still containing living 
embryos after months, or even after years, of cultivation. Epstein 
(3), in Prague, infected children with eggs that had been kept in 
culture for a year. Davaine (1, 2), in France, in the second half of 
the 19th century, carried out his classic experiments with rats to 
which he fed Ascaris eggs that still contained viable embryos that 
hatched in these rodents, despite the fact that the eggs had been 
maintained in culture for 5 years. 
At temperatures near freezing the development of the eggs does 
not progress. If development already has begun, it comes to a stand- 
still at a temperature a few degrees above freezing, only to be resumed, 
however, when the temperature rises. The eggs are resistant, more- 
