171 



Microscopic serial sections made from alcoholic specimens show best 

 the changes which have taken place in the surrounding tissue; On 

 Plate XXVI, Fig. 2, there is figured an enlarged view of one of the 

 worms still encysted and surrounded by the tumor of inflammation. 

 From this section it is seen that the irritation setup in the adjoining con- 

 nective tissue causes the cells to proliferate and crowd closer and closer 

 together. It is also seen that there is a special cyst for the worm and 

 a thickened adjoining portion of the tumor which is like a surround- 

 ing membrane. As these two membranes, the so-called cyst and the 

 outer one, stain so nearly alike, it has occurred to me that they represent 

 successive efforts of the adjoining tissue to protect itself against the 

 parasite; but in view of the fact that the inner one is so easily enucle- 

 ated, it is for the present considered as belonging to the worm. At the 

 foot of Plate XXV, Fig. 8, there is given an illustration of a small 

 tumor in which the worm has escaped from the cyst and in which the 

 surrounding matter has become cheesy, some of it even hard. Around 

 the entire mass the tissue is slightly thickened and forms a capsule. 



From these two microscopic sections we can learn how these tumors 

 grow. The worm penetrates to the submucous tissue and irritates it. 

 The adjoining cells rapidly increase in number and crowd upon each 

 other. So closely do they crowd and so numerous do they become, that 

 the outer layers cut off the circulation from the inner cells and they 

 die. Their degeneration gives rise to the cheesy mass. Ifow, if the 

 worm remained in the center of the mass the new growth would event- 

 ually cease, but the worm makes its way to the outside and at that 

 point keeps up this irritation and new^ growth. This is shown by and 

 accounts for the dried older parts of the larger tumors and the fresh 

 yellowish-green adjoining parts. As soon as the worm escapes the irri- 

 tation ceases, the tumor shrinks, and absorption of the mass begins. The 

 irritation produced by the worm provides it with food and favorable 

 surroundings for development. Often the worm dies from weakness or 

 other cause, and leaves behind those little hard incompletely-grown 

 tumors which have been mentioned. 



Since writing the above life history two post-mortem examinations 

 have been performed, which lead me to modify my views regarding tlie 

 life history of certain other tumor-making parasites. On August 10, 

 1889, two lambs, one five months old, the other eleven weeks old, died. 

 The older lamb was bred at the experimental farm ; the younger was 

 bought with its dam when but a day or two old. These lambs had no 

 water save what was pumped from a well. Among other parasites, 

 each species being found in its proper portion of the intestine, there 

 were numbers of individuals of (Esophagostoma scattered through the 

 length of the large intestine. These individuals were of all sizes, from 

 the smallest stage (T"""" long) to those nearly adult. In the younger 

 lamb there were but few very minute tumors in the coats of the large 

 intestine. In the older the tumors were somewhat larger, but none were 



