Nov. 25, 1918 Observations and Experiments on Intestinal Trichince 47 1 



alive in a physiological salt solution for a number of days without their 

 undergoing any growth changes. These larvae must have been in the 

 small intestine for at least several hours, yet their larval condition 

 remained unaltered and they were capable of living for several days in 

 a salt solution. In view of these facts and in the light of what will pres- 

 ently be described with reference to the behavior of the intestinal para- 

 sites which have begun further development, it is apparent that the 

 effects of natural gastric digestion on the larvae is very much like the 

 effects of artificial digestion; that is, the parasites are liberated from 

 their cysts, but are not stimulated to further development. 



CHANGES IN THE BEHAVIOR OF THE DEVELOPING LARVAE 



As has already been stated, larvae taken from an artificial digestive 

 medium after a period of incubation of 18 hours are quite active. Even 

 after being washed in a physiological salt solution several times, the para- 

 sites still exhibit movements at room temperature. Gradually they 

 become sluggish, the posterior end of the worm ceasing its contractile 

 movements entirely, while the anterior end may still exhibit feeble 

 activity. The worms finally coil up tightly and lapse into a quiescent 

 condition, which characterizes these parasites in their normal locations 

 in the voluntary muscles of the host. 



In comparison with the quiescent state of the intact larvae at room 

 temperature the sexually mature and the maturing parasites taken from 

 the small intestine and kept under observation in a physiological salt 

 solution present a marked contrast. The intestinal forms continue 

 their movements with almost unabated vigor until they succumb. 

 Their activities are not as feverish as those of the intact larvae which have 

 been artificially stimulated, but are more persistent, more regular, and 

 independent to a considerable extent of any external stimulation. Under 

 none of the conditions to which they were subjected have the intestinal 

 trichinae been observed to coil up. Not even the depressing temperature 

 of a refrigerator (10° C.) caused them to manifest the least traces of 

 becoming coiled. The cold rendered them temporarily rigid, but they 

 remained either completely elongated or exhibited a sinuous outline. It 

 was quite evident that the low temperature paralyzed their movements, 

 leaving each individual in the posture which it had assumed prior to 

 coming under the influence of the cold. 



It appears, therefore, that in addition to certain morphological differ- 

 ences the intestinal forms may be readily differentiated from the intact 

 larvae by their behavior in vitro. This is not the only physiological 

 criterion, however, which can be employed to distinguish the maturing 

 forms from the encysted larvae. The latter have been known for a long 

 time to have marked powers of resisting various toxic agents, in which 

 respect they also stand out in sharp contrast with the developing forms. 



