PRESIDENTIAL ADDRESS — SECTION D. 81 



Kobayashi worked out the development of Clonorcliis day by 

 tlay in infected cats and gave a most valuable account. The 

 infected piscine hosts were those used for food in Japan, and by 

 •experiments he determined that the usual modes of cooking the 

 fish, such as short boiling or roasting, or merely soaking in 

 vinegar and soy sauce (a common method of preparation) do not 

 kill the cysts. 



The source of infection of the various fishes was not deter- 

 mined till 1918, when a paper by M. Muto appeared. He 

 investigated the trematode parasites of various molluscs and fish 

 in Japan. In the mollusc, Bithynia striatula var. japomca, 

 sporocysts were found that gave rise to cercariee that encysted 

 in the fish, Pseudorasbora parva. The fish thus infected were fed 

 to dogs and mice and adult Clonorchis sinensis produced. Muto 

 went further. He infected some Bithynia with miracidia hatched 

 irom the eggs of Clonorcliis sinoisis and obtamed sporocysts and 

 cercariae identical with those found in nature, the sporocysts 

 being produced about three weeks after exposure of the snails to 

 the miracidia. 



The life-history, then, is complete. Ova of Clonorchis are 

 passed with the faeces of infected persons or animals. If they 

 reach water the miracidia escape, and should they reach the 

 water snail, Bithynia striatula, they penetrate and develop into 

 sporocysts in about three weeks. From the sporocysts cercariae 

 are produced that enc3'st on the gills or in the muscles and liver 

 of certain Cyprinidae. The cysts, consumed with raw fish, in 

 the fresh or dried condition, develop into Clonorchis sinensis in 

 man, dog, cat, pig and rat. About 26 days after ingestion of 

 the cysts, ova of the flukes appear in the faeces of the final host. 



It may be mentioned that Muto has found that about aO 

 per cent, of the rats in infected districts in Jajian harboured 

 Clonorchis sinensis. 



Formerly two species of Clonorchis were differentiated, 

 C. sinensis and C. endemicus . Kobayashi has now shown that 

 the two supposed species are but age and growth variations of 

 Clonorchis sinensis, and the species C. endemicus disappears. 



It has been found in the United States that a large propor- 

 tion of the Chinese entering the coimtry are infected with 

 Clonorchis. Thus, in 1916, of 604 Chinese innnigrants arriving at 

 San Francisco, Gunn found that 125 harboured the parasite. 



The molluscan hosts are species of Bithynia, which is very 

 widespread and is found in China, Japan, Indo-China, Dutch 

 East Indies, Africa and Southern Europe. Members of the 

 Cyprinidae are also practically cosmopolitan. There is thus a 

 possibility of Clonorchis estabhshing itself in South Africa, while 

 the importation of Chinese fish by the Chinese for their own 

 consumption (as occurs in South Africa) provides another source 

 of infection. 



It is of interest to note that a number of cases of Clonorchis 

 infection associated with carcinoma of the liver have been 

 recorded, including the recent case in Johannesburg. 



