Nov. i, 1920 Control 0} Fluke Diseases 195 



Paragonimus in Formosa in 191 6 (13) have given a definite basis for 

 preventive measures against all these parasites of man and of the related 

 parasites of domestic animals. 



In every case of fluke infection of man or domestic animals in which 

 the life cycle of the parasite has been worked out it has been shown that 

 fresh-water snails act as necessary intermediate hosts. It appears, there- 

 fore, that if some efficient and practical method of destroying the snails 

 could be found, this would furnish a logical point of attack in the control 

 of all fluke diseases. Other preventive measures are, of course, valuable 

 also and could be used as supplementary measures — for example, the 

 impounding of water before use for drinking or bathing as a preventive 

 against Schistosoma infections, the discouragement of the habit of eating 

 improperly cooked meat of crabs in the case of Paragonimus and of fish 

 in the case of Clonorchis, and care in the disposal of feces and urine in all 

 cases. The last, exclusive of individual mechanical protection against 

 infection, is the only preventive measure that can be adopted against 

 hookworm and many other intestinal parasites. To accomplish this in 

 some warm countries where there has never existed anything approach- 

 ing sanitation and where the very idea of sanitation is so strange and 

 foreign to the habits of life and thought of the natives is well nigh impos- 

 sible. The fact, therefore, that fluke infections may possibly be con- 

 trolled by attack upon an intermediate host instead of by reliance upon 

 the enforcement of sanitary regulations makes the ultimate eradication 

 of these infections, in spite of their relative incurability, a matter of 

 brighter prospect than is the case with many other verminous parasites. 



Already a number of suggestions for the destruction of the snails which 

 act as intermediate hosts of flukes have been made. Thomas (18) ad- 

 vised the extensive scattering of salt on pastures where sheep were known 

 to become infected by flukes, and he commented on the absence of fluke 

 infestations among sheep grazing on salt marshes. The effect of the 

 salt, of course, was to destroy the snail, Limnaea, which acts as the inter- 

 mediate host. Leiper (10) suggested the eradication of the disease in 

 agricultural districts in Egypt by the intermittent flow of water in the 

 irrigation ditches, the water being turned off for 1 5-day periods, thus 

 drying up the ditches and destroying the snails by desiccation. Such 

 a procedure is, of course, very limited in its application, and in view of 

 the remarkable resistance which many snails have to drouth it is doubtful 

 whether all the implicated species could be killed by this method even if 

 it were feasible. Leiper suggested that ammonium sulphate be applied 

 to pools which were inhabited by the intermediate hosts of Schistosoma. 

 Lime has been recommended by a number of writers, particularly 

 Japanese, as the cheapest and best method of destroying snails. One 

 Japanese writer, Ando (1) states that 1 per cent lime water killed 6 of 10 

 snails in seven hours, and a 1 per cent solution of copper sulphate would 

 kill them in six hours. It is obvious that none of the above methods of 



