228 THE ORIGIN AND PROPAGATION OF DISEASE. 



1834, by the Corsican student Eenucci, and the study of its structure 

 and development was afterward accoinplished by Easpail and Bour- 

 guignon ; so that our knowledge, both of the disease and its parasite, 

 was then placed upon a permanent footing. 



Perhaps the most suggestive part of this discovery related to the 

 reproduction of the parasite, the manner in which the female lays her 

 eggs in galleries excavated in the skin, and the time required for the 

 hatching and dispersion of the young, because this showed a direct 

 connection between the local spread of the disease and the increase, by 

 ordinary sexual generation, of the young brood of the parasite. How- 

 ever, there was nothing very remarkable in the mode of this genera- 

 tion. The eggs of the female were deposited and hatched in the usual 

 way, and the young sarcojjtes came to resemble their parents after a 

 very short and regular period of development. 



But ten or fifteen years later a discovery was made with regard to 

 some of the internal parasites which had a character of unexpected 

 peculiarity; that was, the specific identity of two parasites formerly 

 supposed to be distinct, namely, cysticercus and tmnia. These two 

 worms — so unlike in their size, their general configuration, and even in 

 the species of animal which they inhabit — were shown by the researches 

 of Siebold and Kiichenmeister to be only different stages of growth 

 of the same creature — one the encysted and quiescent, the other the 

 intestinal and reproductive form. The well-known experiments carried 

 on in tbis investigation showed furthermore the regular and natural 

 conversion of these two forms into each other 5 and thus we came fully 

 to understand that the existence of tape-worm in man was owing to his 

 having eaten measly pork containing cysticercus^ and that the pig be- 

 came contaminated with cysticercus by devouring the eggs or the egg- 

 bearing articulations of Timia solium. The knowledge of the alternation 

 of generations and of the migration of parasites from one habitat to 

 another at different periods of their development became in this way con- 

 nected with the i)athology and mode of propagation of certain well- 

 known and perfectly distinct morbid affections. 



But so far, perhaps, these morbid affections hardly deserved the name 

 of diseases. They were simply local disorders, due to the presence of a 

 parasitic intruder in the substance of the skin or in the cavity of the 

 intestinal canal. It was another thing to learn, some years later, that 

 a microscopic parasite might diffuse itself generally throughout the 

 system, and thus give rise to a rapid and fatal train of symptoms hardly 

 distinguishable from those of any febrile constitutional disease. No 

 doubt ca«es of infection by Trichina spiralis have always occurred as 

 frequently as they do now. But previous to the year 1850 the milder 

 ones in all probability were supposed to be rheumatic in their origin, 

 while the fatal cases passed for fevers of a typhoid character. There 

 were even epidemics of the trichinous affection, as there are of typhoid 

 fever and influenza; and, w^hen the true character of the disease be- 



