MICROBIAL DISEASES OF MAN AND ANIMALS. 685 



ease, and the symptoms, produced by a malarial infection, may vary al- 

 most indefinitely according to the precise way in which the host is harmed 

 by the infection. Consequently, an enumeration of the clinical mani- 

 festations of malaria is of less importance to a student than is an under- 

 standing of the way in which the malarial parasites harm their host. 

 The malarial parasites destroy the red cells; consequently, they may 

 cause an anaemia with the symptoms which depend upon it. Secondly, 

 they produce toxins which may cause both acute and chronic intoxications; 

 the acute intoxications are seen in the ague fit and in some pernicious 

 forms of malaria, the malarial neurites are examples of chronic intoxi- 

 cation. Lastly, malarial parasites may do harm by blocking the cap- 

 illaries and causing the death of the cells which are cut off from the cir- 

 culation; the symptoms which result depend upon the functions of the 

 cells which are destroyed. If the disease be long continued, with a high 

 temperature, the degenerative changes which usually result from chronic 

 disease and constant fever are produced in the patient. 



The definite diagnosis of malarial fever depends upon the demon- 

 stration, in a patient, of the malarial parasite, or of the pigment produced 

 by it. 



Quinine is the only drug which has a specific action on the malarial 

 parasite. It must be given thoroughly and in full doses. 



Malaria is the type of those diseases which are produced by a parasite 

 and transmitted by an insect. Such diseases may be prevented by meas- 

 ures directed, either against the parasite or against the transmitting agent. 

 Malaria is caused by a Plasmodium and transmitted by the bites of 

 mosquitoes belonging to the Anophelince. The disease may be combated 

 by destroying the parasite, in infected persons with quinine, and by 

 isolating such persons behind mosquito curtains so that mosquitoes may 

 never have an opportunity of ingesting the parasites they contain. Ma- 

 laria may also be prevented by destroying the mosquitoes which transmit it. 

 The most efficient way of getting rid of mosquitoes is to make it impossible 

 for them to breed. The eggs of a mosquito are laid in water, and water 

 is absolutely necessary for the larval and pupal stages, which must be 

 passed through before the adult mosquito is produced. Fish destroy 

 developing mosquitoes and large sheets of water are too rough for them; 

 so mosquitoes must have, for breeding, rather small collections of fresh 

 water free from fish. Mosquitoes will soon disappear from a locality 

 if all such collections of water, within a quarter of a mile of it, are filled up, 



