478 Journal of Agricultural Research voi. xv, No. s 



izes the intestinal forms at the various stages of their development. The 

 effects of potassium cyanid on the intact larvae and on the molting forms 

 have been studied especially with a view of determining changes in the 

 resistance of the parasites at various stages of their life history. 



These studies have yielded interesting data which the writer expects to 

 present in a separate paper. The poison causes a disintegration in the 

 tissues of the worms without influencing their general outline, due un- 

 doubtedly to the cuticle remaining unaffected. Moreover, the worms 

 exhibit a differential sensibility to the poison along the major axis, the 

 wave of disintegration in the intact decapsuled larvai starting at the 

 anterior end and proceeding posteriorly. When the head end shows a 

 marked paling of the protoplasm accompanied by the beginning of gran- 

 ular degeneration the posterior end of the worm is normal as to color and 

 transparency. The maturing larvae as well as the sexually ripe specimens 

 taken from the small intestine are not only more susceptible to potassium 

 cyanid and perish almost instantaneously in dilutions in which the decap- 

 suled larvae survive for several hours, but show a complete reversal of 

 axial susceptibility by being affected in the posterior end, the wave of 

 disintegration gradually moving toward the anterior region. In Trichi- 

 nella spiralis the posterior region consists largely of reproductive cells 

 which, as growth takes place in the small intestine, divide very rapidly 

 and produce thousands of germ cells. In fact, the development of the 

 larvae in the small intestine is essentially a sexual metamorphosis 

 characterized by a rapid division of the germ cells and the maturation of 

 the latter, accompanied by the appearance of the accessory reproductive 

 organs. It is rather significant that while these changes are taking place 

 in the larvae the axial susceptibility of the worms to such a depressing agent 

 as potassium cyanid should show the decided reversal described above. 

 In the writer's opinion these facts are a striking confirmation of the 

 views expressed by Child— namely, that there is a direct relation between 

 susceptibility to depressing influences and the degree of metabolic 

 activity.^ 



How can the sudden change in susceptibility of the worms to toxic 

 agents be accounted for ? In view of the fact that even the intact larvae 

 exhibit a differential sensibility to potassium cyanid along their major 

 axis, the cuticle as the all-important factor underlying the resistance of 

 the worms to toxic substances must be eliminated. The fact that the dis- 

 integration of the parasites under the influence of potassium cyanid is not 

 haphazard but follows a definite course is direct evidence that the disin- 

 tegration is a reaction between the tissues and the poison independent of 

 the permeability of the cuticle, and that the rate of reaction varies in 

 different regions of the worm. The reversal of susceptibility in the 



• Child has published numerous papers dealing with this problem. His views are summarized in two 

 books cited in the list of references (r. a). 



