STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 55 



though whites are subject to fever. The symptoms may appear as 

 early as four weeks after infection or as late as seven years. 



"In the second stage trypanosomes appear in the cerebro-spinal 

 fluid and in large numbers in the glands, those of the neck, axillae and 

 groins becoming enlarged. There is tremor of the tongue and hands, 

 drowsiness, emaciation and mental degeneration. The drowsiness 

 passes into periods of lethargy which become gradually stronger until 

 the patient becomes comatose and dies. Some victims do not sleep 

 excessively but are lethargic and profoundly indifferent to all going 

 on around them." 



Late investigations go to show "that Glossina morsitans may act 

 as a host for a human trypanosome which is probably identical with 

 T. gambiense." Probably also " that some of the vertebrates other than 

 man may harbor T. gamhiense and that there is a possibility of these 

 things being transmitted to man" (Doane). 



With regard to the development of T. gambiense in Glossina palpalis 

 it is known that "two days after biting an infected animal the fly 

 becomes mcapable of mfectmg other animals and remains so for about 

 22 to 28 days, when it again becomes infective and may remain so for 

 at least 96 days. During the infection period the salivary glands are 

 found to be invaded with the type of the trypanosome that is found 

 in the vertebrate blood" (Doane). 



Rat Fleas and Plague: 



Plague, known in three forms as bubonic, septicaemic and pneu- 

 monic, is caused by Bacillus pestis which attacks rats, mice, cats, dogs 

 and other animals. The disease is transmitted mainly by fleas, some- 

 times by bed-bugs, and the wounds made by the bites allow entrance to 

 plague bacilli. "Plague is primarily a disease of rats, an epidemic of 

 plague in these animals having often been observed to precede as well 

 as to accompany an epidemic among human beings." 



The recent outbreak of pneumonic plague in Manchuria showed an- 

 other phase of infection. This disease is not dependent on fleas for 

 its transmission, but it could be traced to an outbreak of plague in the 

 tarabagans or marmots, a kind of squirrel. Dr. Cantlie says that Plague 

 may develop or appear in the following stages: (i) as a disease in ani- 

 mals; (2) as pestis minor conveyed by infected insects; (3) bubonic 

 plague, sporadic cases, carried from animals to man by insects; (4) epi- 

 demic bubonic plague carried from man to man by insects; and (5) 



