75 
symptoms, and, moreover, has not given due consideration to possible 
causes of the S3^mptoms other than the presence of Tsenia. A com- 
parison between the 49 cases of II. nano referred to and Seeger’s 
cases is, nevertheless, not unwarranted. Not only in the latter as in 
the former is no attention paid to possible causes in the etiology of 
symptoms other than the presence of tapeworm, but the}^ are in a sense 
selected cases. Seeger’s cases were selected because of the occurrence 
of s^^mptoms, and similarl}^, in connection with the cases of II. nana 
just mentioned, there has been a sort of selection, namely: If symptoms 
had not occurred in nearly all of these cases the circumstance of infec- 
tion with II. nana would not have been discovered; these cases were 
' thus picked out automatically from among pfobabl}^ a large number 
I of cases, the remainder of which were without s^unptoms and thus 
! never came under observation. 
i Severe nervous symptoms, apparentl}^ determined b}- the presence 
j of tapeworm, were present in at least 10 per cent of Cobbold’s cases 
|. (see p. 67). Convulsions were present in onlj^ 3 per cent of Hirsch’s 
I cases (see p. 66), but other phenomena occurred in a considerable 
' number which will allow an estimate of severe nervous symptoms 
in about 10 per cent of the cases. Not more than 12 to 15 per cent 
of all® the cases of H. nana., or 30 per cent of the cases in which 
the presence or absence of symptoms has been definitely reported, 
exhibited severe nervous symptoms attributable with an}" degree 
' of certainty to the action of the parasite. 
A comparison with Seeger’s statistics tends to show that severe 
symptoms are less common in cases of II. nana than in cases of other 
tapeworms, while comparison with the statistics of Cobbold and Hirsch 
indicates that grave nervous disturbances are more common in cases 
of H. nana than in cases of other tapeworms. All of these com- 
parisons are open to criticism, but the first, although perhaps the 
most artificial of the three, probably arrives nearer the truth than 
either of the others, and it may be affirmed that severe effects from 
the presence of Ilymenolepis nana are no more common than from the 
presence of other tapeworms, but on the contrary are very likely much 
less common. The high percentage of severe effects with cases of II. 
nana as compared with cases of other tapeworms is no doubt due, in part 
at least, to the fact that a proportionately greater number of cases of II. 
nana pass unnoticed than of larger tapeworms. The presence of a large 
tapeworm is usually made manifest, sooner or later, by the passage of 
segments, while a microscopic examination is necessary to determine 
the presence of II nana^ and, as already remarked, unless there happen 
to be symptoms which will bring the patient under medical observa- 
tion, in which case a fecal examination may be made, the chances are 
very much against the diagnosis of any particular case among the 
«See footnotes, p. 71. 
