166 DADD'S VETERINARY MEDICINE AND SURGERY. 



abdomen, thorax, and cranium. Their bulk and weight often ex- 

 ceeds that of an ordinary grasshopper ; still you see and hear them, 

 skipping, jumping, and chirruping, notwithstanding this immens*- 

 parasitic mass, just as freely as those not infested. 



Then consider the condition of the hog. We frequently find^ 

 in his liver, a vesicle filled with fluid, apparently possessing no 

 further organization. But examine it carefully, and we shall find 

 within its enveloping tunic others, the rudiments of successive 

 cells, in various stages of growth. These are all young hydatids, 

 which contain still others, which increase in size until the parent 

 sac is so distended that it finally bursts, and thus liberates a mul- 

 titude of parasites, which, in their turn, undergo the same evolu- 

 tion, becoming each a parent hydatid, producing a subsequent 

 generation, which diffuse themselves over the whole body of the 

 pig; and hence arises that peculiar feature in pork known as 

 measles. 



Examine the same animal after he is slaughtered, and you may 

 possibly find in the intestines a large number of the ascaris lum- 

 bricoides (the common worm of the human intestines) ; and they 

 are so prolific that naturalists have calculated sixty-four millions 

 of ova within the body of a single female, which are, at the proper 

 season, deposited within the intestinal tube of the pig, who, not- 

 withstanding, grows fat, and furnishes a savory meal for the lovers 

 of pork. Sheep, also, are infested with a species of entozoa termed 

 the "fluke," besides other different species; and it is only when 

 the latter become very numerous that they can be considered in- 

 jurious. 



We might go on to show that every living being is more or 

 less infested with parasites, and that parasites are, in their turn,, 

 the local habitation for other parasites. The very atmosphere we 

 breathe, and which is the purificator of the vital current (the 

 blood), teems with an innumerable host of living organized crea- 

 tures. The water which serves to quench the thirst, that plays 

 so important a part in our economy, and in the arts and sciences, 

 whether it be the ocean, lake, river, pond, or gully, all contains 

 crowds of parasites, or animalculae, at times, so numerous that 

 several hundred thousand have, by means of a magnifying lens, 

 been discovered in a single drop of this fluid. Yet such is good 

 and pleasant to the taste ; and the water is not injured thereby ; 

 neither is it, in turn, injurious to man. Dr. Leidy states that he- 



