196 THE AMERICAN MONTHLY [September 



of the inner and others as composed of the outer membrane. So far ae 

 I have observed in this specimen, the papilla is composed of the outer 

 membrane, but I hope to investigate this point further and with higher 

 powers. The ova develop slowly, and at the end of several months at 

 the earliest and often not for a year and a half or more a worm-shaped 

 embryo may be found. They have great power of resisting the influ- 

 ence of external surroundings and may be dried or frozen without losing 

 vitality, though their development may be arrested. They are probably 

 introduced into the body by means of food or water. 



So far as the description of the ovum above given goes, it applies 

 perfectly to our specimen, and as I can find no other ovum having this 

 peculiar projection on each end, we may ascribe our ova to T. dispar. 

 Therefore from our study of this slide we conclude that we have to do 

 with the liver of some small carnivorous animal or rodent, several lo- 

 bules of which have been replaced by the ova of Trichocephalus dis- 

 par \ a nematode worm of the family Filarid^e. 



This completes our study. It has been my endeavor to show what 

 may be done with a medium grade instrument, without extra appliances, 

 and with ordinary powers {\\ inch to \ inch), and to show that any 

 slide, carefully studied, will amply repay the time spent upon it. If I 

 have succeeded in demonstrating this I am abundantly satisfied. 



DISCUSSION OF PAPER. 



At the meeting of the Washington Microscopical Society, when this 

 paper was presented, Mr. Smiley said : I am pleased with the manner 

 in which the subject has been treated. By taking one step at a time 

 and giving reasons for each step a subject may be thoroughly explained. 

 This is the method adopted by Dr. James, of St. Louis, in his work on 

 Microscopy, by means of which a beginner may take up microscopy 

 and find every step carefully and progressively explained. 



Dr. Acker said : This method is the one vised by Virchow in his 

 teaching. As to this worm I have seen it commonly in Germany, but 

 I have searched for it carefully in every post-mortem examination made 

 by me at the Children's Hospital in this city, but without success. It 

 is commonly found in the calecum. 



Dr. Balloch said : I was led to treat this slide in this way by my own 

 experience with text-books, which most commonly tell you that a thing 

 is so, but do not say why it is so. 



Mr. Duff showed a fine photograph of Trichocephalus dispar, en- 

 capsuled in the liver of a spitz mouse, which was made by Dr. Gray, 

 of the Army Medical Museum. The ova were magnified 350 diameters 

 and showed the same structure and general appearance as those in Dr. 

 Balloch's specimen. 



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