VERMICIDES AND VERMIFUGES 271 



There are many drugs not included in the above groups which 

 are occasionally used as anthelmintics but as they possess other 

 more important and typical actions they are discussed in other places. 

 Only those drugs which have no other therapeutic action will be 

 discussed here. 



Action of Vermicides and Vermifuges. The ideal anthel- 

 mintic should kill or stupefy the parasites but not irritate the 

 gastro-intestinal tract of the host or be absorbed in sufficient 

 amount to produce harm to the host. No such parasiticide has 

 as yet been found that fulfills these requirements and all are 

 capable of producing disastrous effects if not used cautiously and 

 none of them is of certain action upon the parasite. The remedy, 

 however, must be capable of penetrating the outer covering of the 

 parasite, so that volatile poisons whose vapors permeate the in- 

 testinal canal, penetrate the covering of the parasite and kill or 

 stupefy it, before absorption takes place by the host, fill this require- 

 ment. In many cases the absorption is retarded by the presence of a 

 fixed oil which exists along with the volatile oil. A volatile para- 

 siticide is often combined with a fixed oil simply to retard the ab- 

 sorption of the anthelmintic. On the other hand preparations of 

 volatile substances are always unstable and some uncertainty always 

 accompanies their use. 



In some cases the parasite seems to show a peculiar susceptibil- 

 ity to certain poisons. For instance, pelletierine in very dilute 

 solution (1 — 10,000) will kill tape worms, while santonin is more 

 toxic to the round varieties. 



Active catharsis is a factor in the removal of the parasite but is 

 not sufficient alone, because, if in good condition, the worms are able 

 to move against peristalsis or to attach themselves to the walls of the 

 intestines. 



Before the administration of a vermicide the intestinal canal 

 should be emptied so far as possible by fasting the animal for from 

 12 to 24 hours or by allowing only a light easily digested diet. This 

 procedure weakens the worms and prevents the contents of the in- 

 testines from diluting the medicine or protecting the worms. A 

 purgative should always accompany or follow an anthelmintic be- 

 cause the worms are rarely killed and would recover if left in the 

 intestine. Croton and castor oil are often prescribed as the purga- 

 tive although, according to Poulsson, castor oil should not be ad- 

 ministered with aspidium because it tends to aid its solubility and 

 absorbability. Other authorities dispute this and claim that oils aid 

 in the solution of the active principles ; but the records show that in 

 most cases of poisoning in man, the remedy has been administered 

 with or followed by castor oil. 



