Trichinellidae 169 



Under natural conditions larvae liberated in the stomach soon make 

 their way to the intestine where they mature in upwards of 48 hours. 

 The isolation of intestinal forms may be achieved with little difficulty. 



Nearly grown rats are maintained without food for 48 hours and are 

 then each fed separately a thumb-sized piece of heavily trichinosed tissue. 

 At the desired time (after 48 hours to get early adults) an animal is 

 killed with chloroform and the intestine removed to a stender dish con- 

 taining warm saline solution. Previous workers have opened the intestine 

 with enterotomy scissors and have searched for the worms in the mucosa. 

 Our method is to cut the intestine, without slitting it, into lengths of 

 about two inches. These are held at one end with forceps and the con- 

 tents stripped out by compressing a second pair tightly against the in- 

 testine near the held end and drawing them downward. The parasites 

 and the slight amount of debris present are caught in a crystal containing 

 saline. The worms may be strained free from the debris using a 40-mesh 

 copper screen, or they may be picked out with a finely drawn pipette. 

 Using this method the author has recovered more than 5,000 adult para- 

 sites from a single rat. 



It is difficult to obtain larvae from the circulating blood. They are 

 small and considerable quantities of blood must be collected, centrifuged 

 and studied before the larvae are found. Fiilleborn accomplished this by 

 centrifuging the blood with a mixture composed of 5% formalin (95 cc), 

 glacial acetic acid (5 cc), and concentrated alcoholic gentian violet 

 (2 cc). The larvae were recovered from the sediment. Using this 

 method Fiilleborn isolated larvae from the blood of the ear and heart until 

 the 20th day after infection. 



It is quite instructive to present, at least for demonstration, larvae of 

 trichinae migrating between the muscle fibers. By killing heavily in- 

 fected animals 18 to 20 days after the initial feeding and compressing 

 small bits of diaphragm between glass plates held together by screw 

 clamps, the larvae near the edge of the tissue are forced free and may 

 be studied. 



The parasites have come to lie in the muscle in their encysted stage 

 2 1 days after infection, and at this point they are again infective. The 

 connective tissue capsule has begun to form and the worms are relatively 

 quiescent. By 35 to 40 days the connective tissue sheath is quite pro- 

 nounced ; this is the best time to obtain encapsulated trichinae. 



By maintaining infected animals, rabbits or cats, for three or four years 

 the ultimate calcified stage may be obtained. 



