424 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



ing numbers of infective larvae, the number of larvae ingested by 

 individual pigs of this group ranging from 1,200 to 35,000. Since 

 a single female trichina may give birth to about 1,000 larvae, the 

 individual pigs in question might have contained from about 500,000 

 up to about 17,000,000 larvae in their muscles. This estimate is 

 based on the assumption that 50 percent of the larvae administered 

 developed into females and that each of the latter developed to fertile 

 maturity and produced a normal brood of young worms. It is doubt- 

 ful, however, that such theoretical expectations are ever realized in 

 the case of experimental and natural infections. It is fairly safe 

 to conclude that pig 6 that received 35,000 infective larvae probably 

 developed an infection characterized by the encystment of several 

 million larvae in its muscles, without exhibiting, however, any 

 noticeable clinical symptoms. 



Although a 200-pound hog (No. 7) was apparently unaffected 

 following the ingestion of 75,000 larvae, two pigs weighing 100 

 pounds (No. 9) and 130 pounds (No. 8), respectively, showed symp- 

 toms, those in the lighter pig being decidedly pronounced and termi- 

 nating in death 7 days after infection. The remaining pigs of this 

 series received doses of from 90,000 up to 174,000 larvae and all of 

 them showed more or less severe symptoms. Each of six pigs (Nos. 

 11 to 16), weighing about 115 pounds and receiving a dose of 100,000 

 larvae, succumbed to the infection at various times between the tenth 

 and twentieth days following the ingestion of larvae. It is interesting 

 to note that the top of the mercury column in the thermometer used 

 in taking the temperature of pig 16, about 1 hour before this animal 

 died, was above the mark 110° F. Pig 26, weighing 90 pounds and 

 receiving 174,000 larvae, showed severe symptoms but it did not 

 succumb to the infection. 



It is evident from these data that infections resulting from the 

 administration of trichinae may be measured by the number of larvae 

 per gram of diaphragm muscle tissue. Applying this yardstick to 

 the data given in table 1, it is clear that in the series of experimental 

 infections under consideration, infections characterized by the presence 

 of up to 900 larvae per gram of diaphragm muscle tissue developed 

 without any noticeable symptoms (pigs 1 to 7). With a single excep- 

 tion (pig 7), however, all the pigs that were found to contain 860 or 

 more larvae per gram of diaphragm muscle tissue did show more or 

 less severe symptoms. 



While the number of larvae per gram of diaphragm muscle tissue 

 bears in a general way a relation to the estimated size of the infecting 

 dose (table 1), particularly in the case of the lighter infecting doses, 

 this relationship is subject to rather wide variations. For instance, 

 pigs 18 to 23, weighing between 150 to 160 pounds at the time of ihfec- 



