50 BACTERIOLOGY 



cocci and Streptococci similarly may cause abscesses, catarrhs, 

 or other forms of inflammation. Dirty or decaying teeth, 

 suppurating gums, enlarged tonsils, and the like are extremely 

 common sites of infection, and proper hygiene of the mouth is 

 one of the best ways of avoiding disease in its many forms due to 

 oral sepsis. In this connection it must be remembered that a 

 toothbrush at once becomes septic after use, and may subse- 

 quently cause infection by scarifying the gums. The brush 

 should therefore be rinsed after use in one per cent, trikresol 

 solution. Some of the many organisms in the mouth or 

 intestine may increase in numbers and attack the tissues and 

 perhaps invade them and even spread throughout the body, 

 producing what is called a septicaemia, i.e. the presence of 

 organisms in the blood ; or they may pass through the damaged 

 walls, say, of the intestine and cause appendicitis or peritonitis. 

 They may thus pass from one position in the body, where they 

 are comparatively harmless, to another where they cause 

 disease. 



Again, bacteria may be inoculated or implanted into the 

 tissues from without. The bite or scratch of some animal with 

 contaminated teetk or claws, or the bite of some blood-sucking 

 insect, are very important means of spreading disease. Rabies 

 or hydrophobia, as is well known, is usually the result of the bite 

 of a mad dog or wolf or other animal itself the victim of the 

 disease. Many diseases, especially those caused by Protozoa, 

 are now known to be carried from man to man or from animals 

 to man or vice versa, by biting insects, which themselves are 

 often necessary for some part of the developmental cycle of 

 the disease-producing organism. Thus Malaria, which causes 

 well over a million deaths per annum in India alone, is due 

 to at least three closely-allied protozoal parasites (see p. 88), 

 which require, in order to complete their development or life- 

 cycle, to pass part of it in certain mosquitoes by whose bite 

 the disease is communicated to man. 



Sleeping Sickness, now spreading and causing such havoc 

 among the negro races of Africa, is caused by a flagellated 

 protozoon known as Trypanosoma gambiense (see p. 85), which is 

 carried by a biting fly called Glossina palpalis and allied species ; 

 whilst a similar trypanosome, T. brucei, which causes Nagana 

 or tse-tse fly disease, and works havoc among horses and cattle 

 in certain parts of Africa, is carried by Glossina morsitans, the 

 tse-tse fly. Numerous other diseases among warm-blooded 

 animals which are caused by other trypanosomes are spread 

 by biting insects, usually a fly, but sometimes a flea or a louse, 

 as in the case of the rat trypanosome (T. lewisi), or by a leech 

 in the case of fishes. 



