90 PRESIDENTIAL ADDRESS — SECTION D. 



Ticks as transmitters of the pathogenic Babesise, Theileria 

 and Spirochaites are well known. Kecently a wood tick, 

 Derniacentor venustus, has been found to be the cause of motor 

 paralysis of the flaccid type in human beings, children being most 

 comnionly affected. The bite of the tick may even cause death, 

 and McCormack has noted that such occurs from respiratory 

 paralysis. It is obvious that tick destruction is necessary for the 

 elimination of spirochaetosis in man and birds, of human tick 

 paralysis and of the numerous piroplasmoses, anaplasmoses and 

 East Coast fever in domestic animals. 



Tsutsugamusi, or Japanese river fever, has been shown to 

 be due to infection with the red mite, Trombidiuvi akamuahi, 

 the life-history of which has been worked out. Miyajima and 

 Okumura* (1916) are among the more prominent workers engaged 

 on the problem, though many others, Kawamura, Nagayo, 

 Miyakawa, Tanaka, Mitamura and Imamura in Japan and Hatori 

 in Formosa have contributed largely to the subject. 



The bites of the larvae of the red mite, TrombuUiun 

 akarnvshi, were known to cause river fever. Miyajima considered 

 that the bite per se was not the cause of the fever, but that 

 some virus was conveyed by the mite. The larvae nourish them- 

 selves on the wild rat, which was believed to be the source of 

 the virus. Efforts to rear the nymphs from larvae apart from 

 the rat were for a long time unsuccessful. Then, in 1916, Nagayo 

 and his colleagues announced the discovery of the nymph, and 

 shortly after Kawanuira and Yamaguchi reported that they had 

 bred the adult from the nymph after one moult. Miyajima and 

 Okumura announced the same result a week later. 



Hexapod larvae removed from the ears of rats and placed in 

 wet sand penetrated into the sand, and in 8 to 15 days became 

 octopod nymphs. In 4 to 6 weeks later, the nymphs meta- 

 morphosed into adults. Meanwhile other observers, of whom 

 Tanaka should be mentioned, had found that two forms of red 

 mite occurred on wild rats, one having small hairs, the other 

 having large hairs. He considered that the small haired form 

 was the true carrier of river fever and that the large haired form 

 should be excluded. Nagayo, however, said that such differences 

 were not specific, but were included within the limits of natural 

 variation within the species. Miyashima then produced the 

 disease in monke,ys, using red mites that he reared from eggs, 

 and the said mites corresponded to the large haired or wild 

 mite. Miyajima and Okumura endeavoured to prove next 

 whether there were one or more species of mite connected with 

 river fever. Examination of large numbers of specimens failed 

 to show intermediate forms, hence there were either two species 

 or dimorphism occurred. The adults of the red mite showed 

 no differentiation, and sexual dimorphism could not be invoked, 

 the larvae having no sexual organs. It was found, however, 

 that no large haired forms could be obtained except in the spring 

 and early sununer. Collections of mites from other sources gave 

 similar results, anci it was thus shown that local differences could 

 not account for the two kinds of mite. The final conclusion 

 reached was that seasonal dimorphisin occurred, the sniall haired 



• See review in China Medical Journal, 1917. 



