DISEASE DUE TO SPIROCHETES 225 



in many of its symptoms, but is due to the presence with- 

 in the lungs of mold-like fungi instead of bacteria. 



Disease due to Spirochetes. — The spirochete is an 

 organism spiral in form. One can be imagined on a 

 large scale by supposing a bit of string to be wound round 

 the finger and the finger withdrawn without disturbing 

 the string. The commonest spirochete disease is syphilis 

 (Fig. 57). The poison of this disease is very injurious 

 to living tissues, so that bad sores are early consequences 

 of the infection, and wide-spread destruction, particu- 



¥ 



Fig. 57. — A Common Kind of Spirochete. 



larly of part of the spinal cord, a later manifestation. 

 Although curable, syphilis is extremely stubborn, so that- 

 only skilful and thorough treatment eradicates it com- 

 pletely when it once becomes established within the body. 



Diseases due to the Filterable Viruses. — Many of 

 the commonest diseases, such as measles and scarlet fever, 

 are due to organisms too minute to be seen under the 

 microscope. A characteristic of many of them is that 

 they- are directly contagious, that is to say, simple contact 

 with the patient often sufl&ces to cause one to become 

 infected. 



Protozoan Diseases. — Malaria is a good example of 

 disease due to a one-celled organism (Fig. 58) which is 

 known to be an animal. This organism establishes itself 

 in the red corpuscles and by interfering with their func- 



