Parasitism and Pathogenesis 659 



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A. Plants Pathogenic for Animals 



Bacteria (Fig. 34) may cause such diseases of man as typhoid fever, 

 tuberculosis, leprosy, botulism (a type of food poisoning), undulant fever 

 (brucellosis), boils, diphtheria, pneumonia, scarlet fever, gonorrhea, men- 

 ingitis, whooping cough, tetanus (lock jaw), and many others. Bacteria 

 produce diseases in many ways by the production of injurious substances 

 which may tend to overcome the defenses of the body to infections or 

 which may destroy tissues or impair their normal capacities to function 

 properly. Certain bacteria produce a substance by which red blood cor- 

 puscles are broken down by the process of hemolysis (he -mol' i sis) (Gr. 

 hiama, blood; lysis, loosing). Certain bacteria (staphylococci, strepto- 

 cocci, pneumococci) produce substances known as leucocidins (luko- 

 si'din) {leucocyte; L. caedere, to kill) which destroy leucocytes (white 

 blood corpuscles). Certain organisms (certain streptococci) dissolve 

 blood clots. In certain staphylococcic infections thrombi (blood clots in 

 vessels) are formed. Certain types of bacteria (including staphylococci, 

 streptococci, pneumococci, and the rod-shaped, anaerobic bacteria asso- 

 ciated with gas gangrene) produce a substance which affects the per- 

 meability of tissues so that materials will readily diflfuse into surrounding 

 tissues. Sometimes organisms block the blood vessels to produce damage 

 either directly or indirectly. Bacteria may also influence disease produc- 

 tion by the use of oxygen, and by the formation of acids, gases, and other 

 detrimental products of metabolism. In some diseases the bacteria pro- 

 duce bacterial toxins ("poisons") which are water-soluble proteins and 

 are extremely potent. Compared with some of them, the poison strych- 

 nine is rather mild. 



Bacteria may produce in other animals such diseases as Bang's disease 

 (contagious abortion or brucellosis) in cattle and other animals, tubercu- 

 losis in cattle, hogs, and other animals, tularemia ("rabbit fever") in 

 rabbits and other similar animals, "lumpy jaw" in cattle, plague in rats 

 and other animals, "black leg" in cattle, "limber neck" (botulism) in 

 chickens, chicken cholera, glanders in horses, sheep, and goats, and an- 

 thrax ("wool sorter's disease") in sheep, horses, goats, etc. 



Fungi may produce in man such diseases (Fig. 74) as actinomycosis, 

 ringworm of various types, including "athlete's foot," aspergillosis (caused 

 by certain species of Aspergillus) , maduromycosis (madura foot), coc- 

 cidioidomycosis (valley fever), etc. 



