History of the Nematode Worms. 459 
certainly aid them in breaking out of the egg-envelopes. More- 
over it is not difficult to ascertain that the firmness of the egg- 
shells considerably diminishes in course of time. 
Nevertheless I have not been able to effect the exclusion of the 
embryos of Trichocephalus and Ascaris, either in water or in moist 
earth. Even the addition of putrefying substances (such as fruit, 
potatoes, and beet) produced no result. It is true that during the 
investigation (especially with Ascaris) we sometimes find a few 
ruptured egg-shells, and even free embryos, but always in such 
small quantity that we remain in doubt whether their exclusion 
has been effected by the mechanical treatment of the objects or 
by the activity of the embryos. By far the greater part of the 
embryos remain within the egg-shells, and die there after a 
longer or shorter period. 
The duration of life in the embryos seems to be longest in the 
species of Ascaris, which may not unfrequently be observed lively 
and mobile in their envelopes after the lapse of a year. Davaine 
states that he saw a portion of the embryos alive even in ova of 
five years old. In my experiments, however, decomposition 
commenced sooner, especially in the earth, where only a few 
living embryos could be detected after the lapse of fourteen 
months. 
The embryos of Oxyuris vermicularis died within a few days, 
without any change of form, whether the ova were kept in water 
or in damp earth*. 
Of course the only thing that remains to be done is to employ 
the mature ova with living embryos for the purpose of experi- 
ment. Starting from the assumption, already repeatedly ex- 
pressed, that these ova could become developed at once in the 
ultimate parasite-bearer into the definitive worm, I made experi- 
ments in their administration several years ago. For this pur- 
pose I chiefly employed Ascaris marginata. The result was 
always negative. The dogs, which were killed at from six to 
twenty-one days after the administration, certainly often con- 
tained A. marginata, but always under circumstances which ex- 
cluded all notion of their having possibly originated from the 
germs administered. I had no better success with A. mystax 
and A. megalocephala, or with A. lumbricoides, the ova of which 
were repeatedly administered to children by a surgeon of my 
acquaintance, and were twice swallowed in large quantities by 
adults. 
Notwithstanding these constantly negative results, certain 
observations on the occurrence of the Ascarides led me to resume 
* This applies also to the ova of Oxyuris ambigua of the Rabbit, which 
are deposited at the commencement of segmentation, and cannot be brought 
to any further stage of development. 
