22 THE MICROSCOPE 



our organism, inflicting upon us more or less serious and some- 

 times fatal disorders, and many peculiarities of the life of these 

 gentlemen have been revealed to us by the microscope. 



No doubt, most people have heard of certain unpleasant 

 organisms, called tape-worms, which are in the habit of taking up 

 their residence in the intestinal canal, and which, if they once 

 settle down on their estates, are as difficult to dislodge as an 

 Irish tenant-farmer. The microscope has revealed the following 

 peculiarities in the life of these uncomfortable guests : — The 

 ordinary Human Tapeworm*" consists of a head provided 

 with a ring of four suckers, by which it attaches itself to the 

 mucous membrane of the intestines, and then proceeds to deve- 

 lope a number of joints, each of which contains innumerable 

 eggs, the whole creature being sometimes 20 or more feet in 

 length. There may be as many as 1,200 joints, and each joint 

 may contain 30,000 eggs. Each of these microscopic ova is 

 covered with a little leathery capsule containing a minute embryo 

 in its interior, and if one of these little ova be swallowed by a 

 warm-blooded animal (in this case the cow) the embryo is set free, 

 and soon bores its way through the walls of the stomach of its new 

 host by means of little siliceous hooks. Having reached a 

 suitable locality, it surrounds itself with a cyst, and developes 

 from its hinder end a kind of bladder, and is now a Cysticerciis^ 

 or Bladder-worm, embedded in the muscles, and constituting 

 the diseases known in animals as measles. In this state, it may 

 remain for an apparently indefinite time, being incapable of 

 producing eggs ; but if a piece of measly beef (not sufficiently 

 cooked to destroy the life of the Cysticercus) is eaten, the bladder- 

 like part is digested, the young tape-worm is liberated from its 

 cyst, and attaches itself by its suckers to the mucous membrane 

 of its new host, and from its end developes a new tape-worm. 



Different forms of tape-worm select different animals for their 

 hosts. Thus another, which infests man in its adult state, shows a 

 preference iox pork in infancy, and in its cystic form is developed 

 in the pig. The tape-worm of the cat is the adult bladder-worm 



* Tccnia vudiocandlata, according to Cobbold, is the most common in man, 

 and passes its immature state in the ox. 



