256 CIVIC BIOLOGY 



parasite of malaria that aroused the scientific world to ihe 

 possible importance of this subject. This was about the time 

 Koch demonstrated the tubercle bacillus as the cause of con- 

 sumption ; but while bacteriology has made enormous prog- 

 ress, owing to definiteness of form and ease of culture of 

 most bacteria, the growth of protozoology has been compara- 

 tively slow because it has been so difficult to distinguish 

 animal cells in and among animal cells, and so hard, or im- 

 possible, to discover methods of cultivating the protozoan 

 parasites in artificial media. Probably most infectious dis- 

 eases the parasites of which are still unknown smallpox, 

 yellow fever, measles, scarlet fever, spotted fever, typhius 

 fever, infantile paralysis, foot-and-mouth disease are caused 

 by protozoa. 



Amoeba of dysentery Entameba histolytica. This parasite is said to 

 have killed more northern soldiers during the late war than bullets. 

 It is most active in the tropics, but is not rare in temperate zones. It is 

 carried in drinking water and on vegetables that are eaten raw. 



Rabies, or hydrophobia. The evidence, while not entirely conclusive, 

 points to a protozoan present in the saliva of rabid animals as the canst- 

 of this disease. All mammals are susceptible to the virus, which attacks 

 the nervous system, following up the nerves from a bite or scratch of 

 a rabid animal until it finally reaches the brain. The animals trans- 

 mitting the infection, in order of decreasing severity, are the wolf, cat, 

 dog, skunk, and other domestic animals. In case of a suspicious bite 

 the brain or head of the animal should be immediately sent to a phy- 

 sician or to the nearest laboratory, where the organisms, known as 

 negri bodies, can be quickly demonstrated, if present. As it requires 

 from fourteen to sixty days for rabies to develop in man, there is time 

 for the patient to reach a Pasteur institute for treatment, if the exami- 

 nation indicates that the germs are present. Spread of the disease is 

 prevented by muzzling and confining dogs when there is danger of an 

 epidemic, and it should be more generally understood that control of 

 cats may be equally important- 

 Parasites of malarial fevers Plasmodium vivax, P. malaria, P. immacula- 

 tum or falciparum. The malarial sporozoa are a group of parasites that 

 have thrown a girdle around the earth wider than that of the hookworms, 



