MALARIAL PARASITES 239 



If we know how the bacteria leave the body of the patient, 

 how they are distributed, and how they enter the body of 

 another, we are well equipped to guard against them. 



I . The Means of Elimination from the Body 



A knowledge of the means by which the contagious 

 material leaves the body of the patient is of first impor- 

 tance in preventing the distribution of such material, and 

 this should always be the first point inquired into in the 

 practical study of any contagious disease. There are several 

 different methods. 



The parasites that produce certain diseases do not find 

 any direct means of being eliminated from the body, and 

 when this is the case the disease is not in any proper 

 sense contagious. Malaria is the best example of this 

 class of diseases, and yellow fever is a second. Malaria, 

 chills and fever, and fever and ague are all names for 

 the same disease, produced by a microscopic parasite living 

 in the human blood. Growing there, it develops poison- 

 ous secretions, and these acting upon the body give rise 

 to the symptom of chill followed by fever only too well 

 known in this disease. The parasite is a minute little body 

 (Fig. 69, i) which enters the blood corpuscle. Inside this 

 corpuscle it grows, and finally breaks up into many little 

 bodies, or spores. As soon as the spores are formed, the 

 blood corpuscle breaks to pieces, setting the spores free 

 and at the same time liberating the secreted poisons. 

 These poisons cause the chill followed by fever well 

 known in malaria. The spores may then enter into other 

 blood corpuscles and go through the same history again 



