146 NEMATHELMINTHES CHAP. 



both sexes are found in the intestine of man and many other 

 mammals. They have been experimentally developed in birds, 

 though in the latter the larval forms have never been observed. 

 By keeping such cold-blooded animals as the salamander at a 

 constant temperature, Goujon and Legros succeeded in infecting 

 them, but the larvae perished as soon as the artificial heat was 

 withdrawn. Muscular trichinosis is unknown in fishes, but the 

 sexual form develops in their intestine. 



The adult parasites of the intestine are scarcely visible to 

 the naked eye ; the females are 3 to 4 mm. long and more 

 numerous than the males, which measure 1'4 to T6 mm. 

 The eggs are very numerous, a single female containing at 

 one time 1200, and probably producing ten times as many 

 during her life. The embryos are hatched out within the uterus, 

 and the larvae leave the body of the mother through the 

 generative pore. The minute larvae bore through the intes- 

 tinal walls of their host, and then, either burrowing in the 

 tissues or swept along in the stream of blood or lymph, make 

 their way all over the body, and come to rest most usually 

 in the muscles, but occasionally in other parts. When the 

 larva reaches its resting-place, it either pierces the sarcolemma 

 and establishes itself within the substance of the muscle-fibre, 

 or it comes to rest between and not in the fibres. Here 

 its presence sets up the formation of 

 a spindle-shaped cyst which usually 

 contains but one larva, though any 

 number up to seven have been found 

 in one cyst. Within this the larva 

 may remain dormant for years, the 

 : UBofthecyst gradually undergoing 



ous deposit. Highly magnified, a fatty or calcareous degeneration. 

 (From Leuckart.) Almost any muscle may be affected; 



those most usually infested being the muscles of the diaphragm, of 

 the shoulder-blade, and of the lumbar region ; the larvae have also 

 been found in the heart. The ends of the muscles near their 

 points of attachment are always the most thoroughly infested. 



The number of the encapsuled larvae in one host is enormous. 

 Leuckart counted between 12,000 and 15,000 in a gramme of 

 muscle, which would give a total of thirty to forty million para- 

 sites in one host ; other estimates place the total even higher. 



