DR. THEODOK NEUMANN. 235 



ground-water or are scattered by the rain, and tlie 

 larvae contained in it, which need moisture, find thus the 

 best opportunities for growth; very easily they have 

 a chance to be introduced into human beings again, for 

 bricklayers, farmers, gardeners, and all such as come in 

 contact with earth and water cannot help getting dirt 

 on their fingers, and as they are when eating not often 

 so scrupulously cleanly as is necessary to prevent the 

 worms from gaining admission into the alimentary 

 canal, as they drink the water without caring what is 

 in it, they introduce incessantly young worms into their 

 intestines. No wonder that under such circumstances 

 an enormous quantity of parasites may be accumulated, 

 and that the danger for all fellow-workmen is great. 



The return of the young parasites into their host is 

 possible only if there are close relations between the lat- 

 ter and the temporary place of sojourn of the former; in 

 other words, the host must at least once in a while come 

 in direct contact with the water or the earth where the 

 embryo is waiting for a transfer. Such conditions are, 

 of course, not always fulfilled, and the prospects for the 

 transportation to a suitable place would be very small 

 for these parasites if nature had not introduced another 

 simple expedient to ward off the dangers possibly re- 

 sulting from such conditions. 



The young parasites are not at once transferred to their 

 final host, but are satisfied with a temporary stay in any 

 animal that just happens to be at hand; they enter into 

 this by active migration or passive transportation, and 

 wait here quietly until they can exchange this tempo- 

 rary place of shelter for their permanent residence. This 

 new host is called the intermediate host, in which the 

 young germs may stay any length of time without, how- 

 ever, obtaining sexual maturity. The latter is possible 

 only in their final host; they must, therefore, be trans- 

 ferred again, which is usually done by the final host de- 



173 



