CLIMA TOLOGY—MTIOLOGY 



1351 



is this danger tiiat the lands have been abandoned, except by ihe 

 very poor, who enter them in order to cultivate hemp or corn, 

 or to gather mulberry-leaves to feed silkworms. The disease is to 

 a limited extent transportable with corn, hemp, and other articles. 

 It occurs most frequently from the middle of July to October. 



According to Weir, a similar disease exists in Korea; to Dowden, 

 in the Malay States; to Schoffner, in Deli; and to Noc and others, 

 at Saigon. 



etiology {vide also pp. 726 and 920). — ^The causation of the 

 disease is not known, but there are three theories which have been 

 supported by various investigators. 



These theories are: — • 



1. The Bacterial Theory. — Many bacteria have been described as the cause 

 of the disease, the first being a Proteus, found by Balz and Takana, associated 

 with staphylococci and streptococci in the lungs, sputum, and urinary sedi- 

 ment. 



2. The Protozoan Theory. — Ogata considers that the cause of the disease 

 is a Plasmodium, which he states he has found in the blood of numerous 

 patients. Ogata's observations have not been confirmed. In 191 7 Hayashi 

 claimed that the parasite was a Piroplasma which existed in monkeys, guinea- 

 pigs, and calves, inoculated with blood from a patient, in the form of granules 

 and rod-shaped, globular, and annular masses in giant cells found in the 

 lymphoid tissue, especially of the guinea-pigs. 



Myashima has found rodlets in the akamushi and in inoculated animals. 



Nagayo, Miyagawa, Mitamura and Imamura state that they have culti- 

 vated an oval, non-capsulated, non-motile organism from patients suffering 

 from the disease. 



3. The Chemical Theory. — Tanaka believes that the true cause is a toxin 

 contained in the body of the mite, and introduced by its bite. 



Fig. 655. — Microtrombidium akamushi Brumpt. 

 (After Hirst, from the Journal of Economic Biology.) 



The only certain facts which we know concerning the aetiology 

 of this disease is that the symptoms follow the bite of the larva of 

 Microtrombidium akamushi Brumpt, and that immunity is not con- 

 ferred by an attack. This larva (akamushi), which, though bright 



