STUDY OF TSUTSUGAMUSHI DISEASE. 11 



counts have • been made to enable us to form an opinion as to their 

 value in prognosis. Anderson reports such a count in a recovering case, 

 the percentages being as follows : Small lymphocytes, 9.9 ; large lym- 

 phocytes, 10.6; polymorphonuclears, 78.7; eosinophiles, 0.3. 



Wilson and Chowning and Anderson described what they considered 

 a Piroplasma in the blood of spotted-fever cases. Later observers have 

 not confirmed this and we do not think that any organism can be seen. 



VII. MORTALITY. 



The mortality in tsutsugamushi disease has been variously estimated 

 at from 15 to 70 per cent or more. Statistics of 567 cases carefully 

 recorded by Dr. Miyajima give an average mortality of 27 per cent. The 

 rate shows a steady and progressive increase from 12.5 per cent in the 

 first decade of life to 57 in the seventh. 



The mortality statistics of tick fever are not based on such a large 

 number of cases and it is probable that many of these which are in- 

 cluded in Wilson and Chowning's tables, but which occurred prior to 

 1902, were not really spotted fever. These authors nevertheless figure 

 the percentage of mortality as 75, and that is approximately correct. 

 This disease is therefore more fatal than the other. So far as the sta- 

 tistics at hand give any indication, the mortality does not steadily 

 increase with the age of the patients. 



VIII. IMMUNITY CONFERRED BY ATTACK. 



One attack of tsutsugamushi disease does not confer permanent immu- 

 nity against another. Probably a temporary immunity is always pro- 

 duced, but second and third attacks in later years are not rare. One of 

 the cases seen by us in August was suffering from his third attack. As 

 a rale, the later attacks of the disease are milder than the first. 



In tick fever second and third attacks are unknown and it seems 

 probable that they do not occur. However, the number of living persons 

 who have had the disease is so small as to make generalizations on this 

 point dangerous. Eicketts says that active immunity of at least two 

 or three months' duration is produced in the monkey or guinea pig by 

 an attack of the disease. 



IX. SUSCEPTIBILITY OE ANIMALS. 



Ogata states that tsutsugamushi disease is inoculable into kittens, 

 apes, mice and guinea pigs. Dr. Miyajima, who has done much work 

 on the subject, maintains that it can be produced in monkeys either by 

 mite bite or inoculation from a patient, but not in mice or guinea 

 pigs. Infected monkeys show fever, but not the skin or genital involve- 

 ment described by Eicketts as occurring in the same class of animals 

 inoculated with spotted fever. Wilson and Chowning thought rabbits 



