166 



account of which Dr. Smith made many tests of the caseous matter for 

 the bacilli both by the microscopical methods and by the inoculation of 

 small animals. In the light of subsequent investigations it is needless 

 to say that these tests had only negative results. In justice to Dr. 

 Smith it should be stated that he undertook the experiments more for 

 negative evidence than from any expectation of flndiug bacilli. 



The cause of the disease is a nematode or ronnd worm, which, though 

 remarkably similar to some other worms of its group, is nevertheless a 

 distinct species from any hitherto described. The failure to find this 

 worm in our earliest investigations may be ascribed to two important 

 factors. The first is that of the season of observation. We had proba- 

 bly overlooked those tumors which were best adapted to show the worms, 

 but mainly on account of the season in which the examination was made. 

 Tlie method of examination was probably the greatest factor in the in- 

 vestigation, for as soon as what may be termed macroscopic superseded 

 microscopic methods the discovery was easy. The method was not en- 

 tirely macroscopic, for simple lenses of low power were used. 



The worms found in the largest tumors were never over 3 or 4""^ 

 in length, and presented only an embryonic development, the vegetative 

 organs alone being present. Figs. 1, 2, and 4, in Plate XXV, were 

 made from the largest specimens. As the adult worms of this class 

 may differ materially from the embryos in the character of the mouth 

 ])arts and in their appearance after the reproductive organs have de- 

 veloped, the difficulty was encountered of connecting the embryonic 

 cystic form with an adult form existing in sheep or elsewhere. 



Determination of adult. — The most conclusive method of determining 

 the adult would be to directly develop an embryo into an adult, but 

 this proceeding was not attempted on account of its difficulties. A less 

 satisfactory method remained of finding some adult worm whose em- 

 bryo was unknown, and which not only corresponded in structure with 

 the embryo, but whose life history was such that it was possible for it 

 to be the parent of the embryo. It will not be profitable to detail 

 theories advanced to aid in this investigation ; suffice it to say that 

 while studying one day a group of worms which came from the large 

 intestines of sheep, I found among them an undescribed species. 



This species was immediately referred to the Solerostominm (Raillet, 

 Mements of Zoologie, p. 330), and later to Molin^s genus (Esophagos- 

 toma. There may be an impropriety in accepting this name over others 

 proposed at the same time for species of this genus, but as the same 

 author proposed them, and as the genus is in general use, it is accepted 

 in this classification. For reasons assigned hereafter in a description 

 of the species I have called it a new one— (Esophagostoma Golumbianum. 

 The specific name is from the fact that the worm was first found in the 

 District of Columbia. 



The adult worm is found in the large intestine of sheep in considera- 

 ble numbers, and in the same animal may also be found the tumors. 



