Nov. 25, 1918 Observations and Experiments on Intestinal Trichince 473 



a retraction of the larva from its cuticle, leaving the latter empty at one 

 end. This is usually observed to occur first at the posterior end. The 

 empty portion continues to increase in size, and gradually the anterior 

 end of the worm begins to contract in the same manner as the posterior 

 end. The worm now assumes the appearance of being incased in a 

 cuticle which is a little too long for it. The head end usually breaks 

 through the membrane and continues lively movements until the entire 

 worm pulls out, leaving the cast-off skin behind. 



It is a significant fact that certain larvae isolated from the small intes- 

 tine as late as 24 hours after feeding the host trichinous meat resume 

 their coiled-up larval posture and do not undergo any further changes 

 when kept in physiologicaf salt solution, whereas others under the same 

 conditions continue their lively movements and undergo a molt. The 

 active larvae have apparently been stimulated by some factors present 

 in the small intestine. Their greater activity at room temperature as 

 compared with that of intact larvae is evidence that their metabolism has 

 been accelerated, and that this change in the rate of metabolism is non- 

 reversible is evident from the fact that the parasites no longer react in 

 the former manner to a lowering of the temperature, but continue active. 

 Their subsequent molting would indicate that the influences under which 

 the parasites resume their processes of growth and morphogenesis are so 

 strong that having once been initiated the reaction proceeds even though 

 the environment under which it normally occurs is replaced by an inert 

 solution of sodium chlorid. The decapsuled larvae prior to their stimu- 

 lation in the small intestine are in a condition of physiological stability. 

 They may, of course, be artificially stimulated to abnormal activities by 

 various physical and chemical agents which if of sufficient intensity and 

 duration soon result in their total destruction. But when the larvae 

 are mildly stimulated, the reactions usually subside shortly after the 

 exciting cause is removed, and the larvae again lapse into a quiescent 

 state. Artificial physical and chemical stimuli, short of those that de- 

 stroy the life of the parasites therefore produce reversible reactions. 

 Under the influence of conditions to which the larvae are subjected after 

 reaching the small intestine of the host animal, a series of reactions is 

 initiated which produce morphological changes in the parasites, leading 

 toward their sexual maturity. These reactions are nonreversible, as they 

 continue for a relatively long period of time in the absence of conditions 

 that brought them about. 



The molting process in the larvae proceeds rather slowly at room 

 temperature. At a lower temperature it may be suppressed, whereas at 

 body temperature it may be greatly accelerated, as the following experi- 

 ment will show : 



Larvae were obtained from a rat within 24 hours after feeding trichinous 

 meat. A few parasites were placed in each of three watch glasses con- 

 taining a physiological salt solution, and kept, respectively, in an incu- 



