THE WEB OF LIFE 365 



folliculorum), generally regarded as a trivial parasite of the 

 human skin, may pave the way for some skin diseases. 

 One of the hints we have alluded to is Dr. Dahl's announce- 

 ment of a new mite, Tarsonemus hominis, found by Dr. 

 Saul in two cases in a human tumour. Was it simply a 

 parasite in the tumour, or had it a share in causing the 

 growth? It is well known that some of the species of 

 Tarsonemus cause gall- like cell-proliferation in plants. 



Yellow fever, or ' yellow Jack ' as it used to be called, is 

 a dread disease that used to break out on ships sailing to 

 West Africa, the West Indies, and the like. It has occa- 

 sionally occurred in English and French ports, and at times 

 severely in New York and Philadelphia, but it is practically 

 confined to between latitude 40 N. and S. and longitude 20 

 E. and 100 W. The fell disease is transmitted by a 

 kind of mosquito, Stegomyia fasciata, which is almost 

 world-wide between the parallels of latitude 40 north 

 and south, a fact of incalculable human importance. For 

 if the disease should be introduced into the East, for in- 

 stance by the opening of the Panama Canal, Stegomyia 

 fasciata is there to spread it disastrously. Fortunately, 

 however, to be forewarned is to be forearmed, and the 

 forearming is now feasible enough. Since the American 

 Commission in 1899 proved up to the hilt what had been 

 previously suggested, that Stegomyia fasciata is the carrier of 

 the disease, the prevention of yellow fever has become 

 possible. The mosquito in question is a ' house-haunting ' 

 insect, and it always breeds near dwellings. The larvae 

 develop in artificial collections of stagnant water, for 

 instance in old pots and pans. If these breeding-places 

 are destroyed, if the mosquito nets and screens are used, 

 and if patients are screened and segregated, so that fresh 



