472 Journal of Agricultural Research voi. xv, no. 8 



as will be shown elsewhere in this paper. The last criterion can therefore 

 be employed as a check on the first to distinguish the early developing 

 intestinal larvae from the intact forms, particularly when the morphologi- 

 cal state following growth in the intestine is not yet sufficiently advanced 

 to warrant a diagnosis on the basis of structure. 



In order to determine whether the change in the behavior of the larvae 

 becomes established coincident with the resumption of growth in the 

 small intestine, the organisms were taken from their hosts within i8 to 

 24 hours after feeding trichinous meat. Upon examination some of the 

 parasites were seen to be in process of molting, and their subsequent 

 behavior at room temperature showed that individuals which have 

 reached the molting stage have abandoned the larval habit of becoming 

 coiled. Of the nonmolting larvae, some continued their active move- 

 ments, whereas others became sluggish and finally coiled up. A number 

 of active forms molted while they were kept under observation, and 

 many of the molting as well as the nonmolting forms succumbed within 

 a few hours. The quiescent forms which became coiled neither resumed 

 their activities spontaneously nor perished at room temperature. Some 

 of these forms were stored in a refrigerator where they maintained their 

 vitality for many days. In fact, they behaved in the same way as larvae 

 obtained by artificial digestion of trichinous meat. 



In view of the fact that certain larvae obtained from the host within 

 18 to 24 hours after feeding trichinous meat may already have molted 

 at least once in the intestine, it is safe to assume that the active larvae 

 which did not molt while they were kept under observation had already 

 cast off their cuticles in the intestine of the host. At least their behavior 

 in vitro showed that they are to be classed with the actively molting 

 forms. 



These observations show that larvae which are in the act of molting, 

 as well as larvae which have molted prior to their isolation from the 

 intestine, have lost the power of assuming the tightly coiled posture 

 which characterizes the intact larvae. They continue their movements 

 until they succumb, and exhibit other traits characteristic of larvae 

 which are definitely known to have molted. Thus they may undergo 

 rapid disintegration when kept in a physiological salt solution at room 

 temperature and exhibit an intolerance for certain toxic substances, 

 which will be discussed elsewhere in this paper. 



MOLTING OUTSIDE OF THE HOST 



Larvae taken from the intestine within 1 8 hours after feeding trichinous 

 meat do not as a rule show any evidence of having molted. If the indi- 

 viduals that continue their movements one or two hours after isolation 

 from the small intestine are carefully observed, the molting process may 

 be studied from its initial stage to its completion. The first evidence is 



