6 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
small sections of uterus and to some extent breaks up the clumps 
of eggs, so that they will spread evenly over the bottom of a petri 
dish. The material thus obtained is then poured into 3 petri dishes, 
enough 2 per cent formalin being added to fill the dishes with fluid 
to a depth not exceeding one-fourth of'an inch. These cultures 
are incubated at a temperature of 33° to 34° C. To secure proper 
aeration of the medium it is stirred with a glass rod every 2 or 8 
days. About one-third of the fertilized eggs will be found to con- 
tain motile, fully developed embryos in 10 days, and practically all 
will be fully developed by the end of a month. 
In using the entire uterus of the worm for preparing the culture 
many incompletely formed eggs are introduced. This may be 
avoided to some extent by using only the terminal portions of the 
uteri, and it is preferable to do so if for any reason it is desired to 
keep the number of incompletely formed eggs in the culture down 
toa minimum. To obtain eggs for the study of their development, 
Wharton (1915) kept the female worms in Kronecker’s solution 
(sodium chlorid 6 grams, caustic soda 0.06 gram, distilled water 
1,000 grams), in which the worms remain alive and active from 6 
to 12 days. The eggs deposited were collected each day from the 
bottom of the vessel in which the worms were kept. 
LONGEVITY OF ASCARIS EGGS. 
Ascaris eggs may remain alive for long periods. Davaine (1863) 
kept the embryos in eggs of A. Jumbricoides alive for 5 years. Mor- 
ris (1911) noted that in human feces which had been kept 2 years in 
2 per cent formalin some of the eggs of A. /wmbricoides present con- 
tained actively motile embryos. Two months later there was an ap- 
parent increase in the number of eggs containing active embryos. . 
Epstein (1892) produced experimental infections with eggs of 4. 
lumbricoides that had been kept in a culture of feces for a year. We 
have kept Ascaris suum eggs alive for many months and there is no 
reason to suppose that the length of time-the eggs of the pig Ascaris 
may retain their vitality is any less than in the case of the human 
Ascaris. Because of the great longevity of the eggs it is evident that 
soil exposed to continual pollution with feces of infested human be- 
ings or pigs may become in course of time very heavily laden with 
living Ascaris eggs. It is also evident that places not exposed to 
fresh contamination may nevertheless retain their infection for years. 
RESISTANCE OF ASCARIS EGGS TO CHEMICAL AGENTS. 
The shells of Ascaris eggs are very impermeable to as well as in- 
soluble in many chemical reagents. Formalin solutions make excel- 
lent media in which to incubate the eggs. A 10 per cent solution of 
potassium bichromate also makes a good culture medium. Many 
