TRANSMISSION OF DISEASES BY INSECTS 267 



Transmission. Whatever the organism may be, the fact is now 

 established that typhus is transmitted by human lice. Nicolle, Comte 

 and Conseil, working in northern Africa (1909), conveyed the disease 

 by the injection of human blood to a chimpanzee; then from the 

 chimpanzee to a macaque monkey; and, by means of human body lice, 

 from this animal to other monkeys. Drs. Ricketts and Wilder 

 performed similar experiments in Mexico City (1910) with similar 

 results. They found that monkeys kept free from lice remained 

 healthy, but contracted the disease after inoculation by means of body 

 lice which had fed on the blood of typhus patients. They showed also 

 the strong probability that infection is transmitted through the eggs 

 to the next generation of lice, which through this indirect infection can 

 cause typhus in monkeys and presumably in man also. It has been 

 found that both the body louse (Pediculus corporis) and the head louse 

 (P. capitis) transmit typhus, but bedbugs and fleas are not implicated. 



The brilliant work of Dr. H. T. Ricketts was cut short by his death, 

 in 1910, from typhus contracted during his experiments. 



Control. A typhus patient is harmless as a source of contagion in 

 the absence of human lice, the agents of transmission. Lice, as is well 

 known, crawl readily from man to man in crowded quarters, and inhabit 

 the clothing as well as the body, particularly the underclothing, the 

 seams of which may contain the eggs in immense numbers. Eradica- 

 tion of lousiness means freedom from typhus. During the World War, 

 Great Britain, France and Germany were successful in protecting their 

 armies from the ravages of typhus by the use of methods, often elabo- 

 rate, directed against the lice, or " cooties." These methods, which 

 are generally known, consisted of (i) the thorough cleansing of the 

 surface of the human body; (2) the disinfection of clothing and other 

 belongings, and of the living quarters, by various physical or chemical 

 processes. 



RELAPSING FEVER . 



Relapsing or recurrent fever is less fatal than typhus, but like the 

 latter is conveyed by lice (though not exclusively) and accompanies 

 war. The disease has often raged in Europe; the last epidemic, early 

 in the recent war, being exceptionally severe in Serbia. 



The cause of relapsing fever is the genus Spirochceta, of which 

 different species produce various types of the disease in different parts 

 of the world. 



