

Seed 



ticks 



THE TICK 



Young 

 adult female 



Engorged 

 adult female 



Female 

 laying eggs 



Bureau of Entomology and Plant Quarantine. I .s.U.A. 



The tick is known to transmit Rocky AAountain fever, or spotted fever, among human 

 beings. Another species transmits the Texas cattle-fever, which was formerly a very 

 expensive scourge in this country. (The ovipositor, on the abdomen, points forward 

 behind the mouth, so that the discharged eggs spread all around the female's head) 



How Do People Become Infected? 



Communicable Diseases Following the methods and the principles 

 developed by Koch, investigators have identified the specific parasites causing 

 some of the most important human diseases, such as tuberculosis, diphtheria, 

 syphilis, typhoid fever, tetanus, pneumonia, malaria, gonorrhea, Asiatic chol- 

 era, bubonic plague and hookworm. These diseases are important because 

 they have again and again killed from a tenth to nearly half the population in 

 great plagues or epidemics. And without flaring up into plagues they have 

 been the greatest causes of deaths, year in and year out, in many regions. 



Common observation and countless experiments with plants and animals 

 leave us certain that the communicable diseases are caused by parasites or 

 viruses. And that they are communicated by the entrance of something mate- 

 rial into the body — either through one of the regular openings to the interior, 

 as the mouth, nose, or urethra, or else through a cut or break in the skin. 



Wounds and Germs For ages common experience had recognized the 

 general fact that wounds fester. Nobody knew why; nor why some festering, 

 or pus-making, ended in healing, whereas other festering was fatal. That is 

 the way wounds act. Whether the skin is broken by a gunshot, a jagged rock, 

 or a surgeon's knife, the two possibilities are present. In hospitals it had been 

 observed that however skillful a surgeon might be, his patients often died as 

 a result of the festering, or "blood-poisoning" as it was called. There was 

 also an excessive number of maternal deaths associated with fever and blood- 

 poisoning. And nobody knew why, nor what to do about it. 



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