APPENDIX J. 



TYPHUS FEVER 



UP till recently all attempts to elucidate the etiology of this 

 disease by ordinary bacteriological methods had given equivocal 

 results. The work carried on by Nicolle in Tunis since 1909 

 has, however, thrown light on the subject. This observer found 

 that the blood of cases of typhus fever during the pre-febrile, 

 febrile, and immediately post-febrile periods, was infective for 

 both the higher and lower monkeys, in the latter especially when 

 introduced intraperitoneally. An illness, frequently fatal and 

 practically identical with the disease in man (including the skin 

 eruption), is originated, and the blood of affected animals is 

 again infective towards fresh individuals. A large number of 

 such passages have been successfully practised. The only other 

 animal susceptible to similar infection appears to be the guinea- 

 pig, in which there arises an illness characterised by rise of 

 temperature and loss of weight, but which is only exceptionally 

 fatal. Neither microscopic nor cultural methods have revealed 

 the presence of any formed causal agent in the infective blood, 

 and when the blood is filtered through a coarse Berkefeld filter 

 it frequently loses its virulence. The causal agent is probably 

 ultra-microscopic, and Nicolle puts forward the view that its 

 retention by the filter may be due to its being entangled in the 

 debris of cells or in colloidal precipitates arising in the filter. 

 The virus is destroyed by a short exposure at from 50 to 55 C. 

 As in the case of man, when an experimental animal passes 

 successfully through an attack of the disease it becomes immune, 

 and although the serum of both men and animals in such 

 circumstances possesses during convalescence slight viricidal 

 properties, these rapidly disappear. There is considerable 

 evidence that under natural conditions infection is spread by the 

 body louse. Monkeys can be readily infected by the bites of 

 lice previously fed on a human case. There is evidence that 

 the causal organism undergoes some developmental stage in the 



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