LIVESTOCK PARASITOLOGY — SCHWARTZ 355 



eluded that many, which by tradition had been regarded as highly 

 efficacious, were actually without merit. They discarded, one after 

 another, most of the older vermifuges they investigated, and gave 

 a nod of approval to only a few, namely, copper sulfate, oil of cheno- 

 podium, oleoresin of male fern, turpentine, and nicotine. Shortly 

 after the publication of these results, Hall introduced into the arma- 

 mentarium of anthelmintics two synthetic substances, both chlorinated 

 hydrocarbons, namely, carbon tetrachloride and tetrachlorethylene. 

 Though these compounds were found to have some application in the 

 treatment of livestock for the removal of helminths, their chief value 

 lay in their efficacy for the removal of hookworms from man and carni- 

 vores. Several related synthetic compounds, notably normal butyl 

 chloride, normal butylidene chloride, and hexachloroethane, also were 

 found to be of value in medicating parasitized livestock. 



Aside from carbon tetrachloride and hexachloroethane, which are 

 still used in treating domestic ruminants for the removal of liver 

 flukes, the chlorinated hydrocarbon anthelmintics, as well as most 

 of the other anthelmintics used earlier, have been replaced to a great 

 extent by more effective drugs. This is due principally to a discovery 

 made in the Bureau of Animal Industry in 1939, concerning the anthel- 

 mintic efficacy of thiodiphenylamine, or phenothiazine. This sub- 

 stance was synthesized in 1885, but lay dormant for many decades 

 before anyone thought of using it for therapeutic purposes. First 

 brought into experimental use as an insecticide and later as a urinary 

 antiseptic, it was found to be of great value in treating horses, cattle, 

 sheep, goats, swine, and poultry for the removal of certain nematodes. 

 Though launched as an anthelmintic only two years before we became 

 involved in World War II, 3 million pounds of phenothiazine were 

 manufactured in the United States for anthelmintic use in 1914, to 

 protect our livestock, especially sheep, from the depredations of 

 roundworm parasites. Today, when our livestock must again be 

 carefully safeguarded as a defense measure, the annual production of 

 phenothiazine in this country is about 5 million pounds, and would 

 greatly exceed that figure if present-day shortages did not limit the 

 volume of production. A number of foreign countries, especially 

 those with large sheep populations, have been making strong appeals 

 to this Government for allotments of phenothiazine or the parent 

 substance, diphenylamine, adequate to protect their sheep and other 

 livestock from parasites in times of emergency. 



Because anthelmintics are more or less specific in their action, in- 

 vestigators working in this field are faced with the responsibility of 

 discovering more effective drugs than are now available for the 

 treatment of specific verminous diseases. Recently, sodium fluoride 

 came into use as a treatment for the removal of ascarids from swine 



