Yellow Fever and Other Diseases 103 



is known to take place in some of these well authenticated 

 cases is presumably true in the case of yellow fever." 



He then goes on to tell how, in various protozoa, 

 the vitality decreases with repeated division until re- 

 production by division will no longer take place. 

 The vitality can be stimulated to a new cycle by 

 artificial means, but, after a time, this too fails and 

 only conjugation will prevent the death of the pro- 

 toplasm. 



He says : — 



" Such artificial stimulation suggests the possibility 

 that in certain human disease, such as malaria, the or- 

 ganisms may become exhausted so far as the division 

 energy is concerned, but may remain quiescent in the 

 system, hibernating, as it were, in some organ until, owing 

 to some change in the chemical composition of the blood, 

 an artificial stimulus renews the division energy and a 

 recurrence follows. 



Turning now to the data that have accumulated in 

 regard to the organism of yellow fever, we must note 

 that the rapid development in the blood indicates that 

 the organisms have been killed off through excess of their 

 own toxins, or by accumulations and actions of the auto- 

 bodies. The long period of incubation in the mosquitoes 

 indicates that processes are taking place in the develop- 

 ment of the germs which can be explained only on the sup- 

 position that conjugation phenomena, analogous to those 

 in the malaria mosquito, are taking place, and this sup- 

 ports the view that in the human blood the organisms are 

 endowed with a high potential of vitality. Again, the 

 filtration experiments, in which it has been demonstrated 

 that the organisms may pass through the finest filters 



