460 Prof. R. Leuckart on the Developmental 
these experiments at different times. In young dogs which 
were still sucking at their mother I repeatedly found these worms 
of from 1 to 2 inches in length, which must consequently to all 
appearance have been living as parasites for several weeks; on 
the other hand, I sometimes observed, in dogs which had been 
shut up for a long time, and fed upon broken victuals, worms 
measuring only a few millimetres, which therefore could not 
long have immigrated. The idea of the probability of a transfer 
in the egg-state seemed the more admissible in the latter case, 
because my dog-kennel was infected by previous experimental 
animals, so that, on microscopic examination, numerous ova of 
Ascaris, m earlier and later stages of evolution, were found on 
its floor. In one of these dogs, some of the Ascarides of which 
were only 3-4 millims. in length, a few ova with developed em- 
bryos were likewise to be found in the stomach. 
In the presence of such observations, the assumption of an 
infection by means of mature ova must acquire more and more 
probability. It is true that experiments in this direction have 
hitherto given only negative results ; but was it quite impossible 
that these were governed by certain individual and temporary 
peculiarities (age, nature of the stomachal fluids, &c.) of the 
experimental animal ? 
Taking these circumstances into consideration, the new expe- 
riments were made under varying conditions. Not only were 
dogs (and cats) of various ages employed, but these were sub- 
jected to experiment sometimes with a full, sometimes with an 
empty stomach, at a longer or shorter period after feeding. 
Unfortunately the result in all these cases was equally nega- 
tive with those of the previous experiments ; and yet the number 
of experimental animals was not less than ten; moreover large 
quantities of ova were always administered, in some cases re- 
peatedly at longer or shorter intervals. The examination was 
usually made soon after the last administration, sometimes only 
from six to twelve hours. In such cases there were usually still 
in the stomach numerous fragments of egg-shells, and even a 
few ova with a clear chorion and disintegrated (or at least deco- 
lorized) contents; but neither a living embryo nor a young 
Ascaris was ever found either in the intestine or in any other 
organ. 
I must admit that it is with difficulty and unwillingness that 
I have given up the notion which served as the foundation of the 
above-mentioned experiments. By the proof that the ova fur- 
nished with mature embryos were developed directly into Asca- 
rides in the intestine of man and the higher animals, the mode of 
occurrence of these worms with all its peculiarities would have 
been both simply and easily explained. But the facts were too 
