418 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 39 



Wandering trichinae have been found also in the mesenteric 

 lymph-nodes, peritoneal cavity, pericardial cavity, pleural cavity, 

 myocardium, lungs, the central nervous system and other locations. 

 In these locations only the young noninfective larvae have been en- 

 countered; the infective larvae are known to occur only in muscle 

 fibers that are surrounded by sarcolemma. While trichina larvae 

 are known to penetrate the tissue of the heart, they are unable to de- 

 velop there and degenerate rapidly. As a result of their penetration 

 into the heart tissue, the larvae produce profound inflammatory and 

 degenerative changes, and these parasites may be one of the factors 

 in cardiac diseases in man and animals. 



It is evident from this account of the life cycle that the entire 

 development of Trichi/nella spiralis takes place in a single host ani- 

 mal which harbors at first the developing and sexually mature worms 

 in its intestine, and later harbors the new generation of worms in the 

 lymph, the blood, and finally in the voluntary muscles. 



FACTS LEADING TO THE DETERMINATION OF THE PREVALENCE OF 

 TRICHINAE IN HOGS IN THE UNITED STATES 



It could hardly be expected that the discovery of trichinae in hogs 

 would be without its effect on the American meat industry, partic- 

 ularly following the alarming outbreaks of trichinosis in Germany. 

 When Europe became trichina-conscious and alarmed, American 

 meat exporters had already carried on for a number of years a brisk 

 trade with various countries on that continent. According to Moh- 

 ler (9) the export trade in bacon alone from the United States to 

 Europe had become well established in 1879. As a result of the 

 trichinaphobia which held the peoples of certain European countries 

 in its grip, restrictive measures against American pork began to be 

 promulgated, Italy, Germany, Austria, and France following each 

 other in rapid succession. The prohibition against American pork 

 was operative in the countries mentioned by 1881. These restrictions, 

 together with the "Slaughter Order" of Great Britain in 1892, which 

 required that cattle imported from the United States be slaughtered 

 at a port of entry because of the fear of contagious pleuropneumonia, 

 are considered by Mohler (9) "as the potent and exciting factors in 

 securing legislation for the scientific inspection of meats for foreign 

 and domestic use, and, incidentally, in advancing the cause of veteri- 

 nary science in the United States." Thus, an observation by Leidy 

 and the subsequent scientific discoveries which followed in its wake 

 were responsible, at least in part, for giving the American people the 

 protection that is afforded by the Federal Meat Inspection Service. 



On August 30, 1890, the Congress of the United States passed an 

 act providing for the inspection of salted pork and bacon, and on 

 March 3, 1891, the Congress passed a more effective meat inspection 



