PARASITIC DISEASES. 335 



especially in sheep, and tens of thousands of these animals 

 are annually destroyed by the distoma. 



A variety of diseases are induced according to the manner 

 in which the parasites lodge in an organ, or according to the 

 peculiarities of the organ itself. Thus echinococchi not un- 

 frequently induce cardiac tumours in the lower animals, 

 attended by all the symptoms of chronic heart disease, and 

 ending in sudden death. Parasites in the cranial cavity lead 

 to paralysis, wasting of the body, and many complications 

 ending also in death. 



Tubular organs are obstructed by parasitic accumulations. 

 Thousands of the calves, sheep, fowls, pheasants, &c., are 

 annually suffocated by round worms in their wind-pipes. 

 Obstructions of the alimentary canal occur in young animals 

 from the accumulation of ascarides. 



I have said that parasites induce ill effects from the man- 

 ner in which they lodge in an organ. The trichinae afford 

 us an excellent example, in penetrating the sarcolemma, and 

 taking the place of the active muscular elements, as described 

 by Leuckart. 



Leuckart has spoken of the usually accepted view, that 

 parasites injure by impoverishing the blood of their victims. 

 He has made an interesting calculation .on the subject. He 

 says, a tapeworm (botriocephalus latus) of 7 metres in length, 

 weighs about 27 '5 grains. It may, during its growth, lasting 

 as it does from five to six months, require from four to six 

 times its weight in nutritive material, but that is of no im- 

 portance to a man. Greater losses are sustained by children 

 when large numbers of ascarides accumulate in the intestines. 

 The only instance of a parasite killing by draining the blood 

 of man is the blood-sucking anchylostoma duodenale (strongy- 

 lus quadridentatus), which attaches itself to the mucous 

 membrane of the intestine of the Egyptians and other orien- 



