PROTOZOA IN CARCINOMA. 191 



be repeated. Thus myriads of young sporozoa are soon found in 

 the alimentary canal, the gall bladder, and the bile ducts of the 

 infected animal. In this stage the organisms are very readily 

 destroyed on being removed from the body, showing a marked 

 difference, so far as resistance is concerned, when compared to 

 the organism in its resting stage. 



The sporules, on being set free from the mother cell, have the 

 power of entering the epithelial cells of the affected region, where 

 they commence a process of growth and differentiation of their 

 protoplasm, which ends in the production of the encysted parasite. 

 It is said that several parasites may infect the same epithelial cell, 

 but, in the adult condition, one parasite is seen to occupy the 

 greater part of the distal region of the cell body, and no trace of 

 others can be seen. In course of time the epithelial cell wall is 

 ruptured, and the parasite escapes, without necessarily causing 

 destruction of the host cell ; it passes through the alimentary 

 canal, gains access to the atmosphere, and thus meets the con- 

 ditions necessary for recommencing the cycle of development. 



Anatomical Changes Produced in the Host. 

 Let me now pass in review the changes produced by this para- 

 site, whose life history I have described, and especially those in 

 the liver where the disturbance is most obvious. The liver of an 

 animal dead of the disease, after the acute stage has passed, or 

 killed when the condition has become chronic, is studded over 

 with greyish-white areas, varying in size from a pin's head to that 

 of a pea, usually rounded, but occasionally somewhat branched in 

 shape, resembling the aspect of chronic tubercle, a likeness which 

 is more close as each spot of disease is filled with material which 

 is apparently caseous. On examining these tumours, however, by 

 means of microscopic sections, they are found to consist mainly of 

 epithelium and connective tissue, which is arranged in the form of 

 a very complex adenoma. The area of the bile duct affected 

 becomes widened, and the space tiius formed becomes filled up 

 with the much hypertrophied and convoluted mucous membrane. 

 The outer margin of the growth is marked off by a layer of well 

 formed connective tissue, varying in thickness from the surround- 

 ing hepatic substance. Lining this fibrous layer is the epithelium 



