78 ZOOLOGY FOR MEDICAL STUDENTS chap. 



of 24 hours are no longer to be detected. However they again make their 

 appearance after an interval of about eight days and are to be found in 

 abundance up till about the nineteenth day all through the haemocoele 

 or body cavity of the louse. From about the nineteenth day the spiro- 

 chaetes undergo a gradual reduction in numbers until apparently they 

 eventually disappear completely and finally. It is during the period 

 mentioned (eighth to nineteenth day) that infection is liable to be con- 

 veyed — not by the bite of the louse, but only in the event of its body 

 being crushed and its infected blood rubbed into a scratch or coming in 

 contact with some part of the skin, such as that covering the surface of 

 the eyeball, through which the spirochaetes are able to make their 

 way. 



Spiroschattdinnta icterohaemorrhagiae is the microbe of epidemic 

 jaundice. It is apparently normally a parasite of the Rat, passing 

 away in the urine and infecting wet soil from which it gains access to 

 the human body either directly through the skin or by being swallowed. 



The last type of spirochaete to be mentioned {Treponema) is that 

 which is the causative agent of the human diseases Syphilis and 

 Yaws. 



The parasite of Syphilis {T. pallida) was discovered by Schaudinn 

 in 1905 and is a minute spirochaete averaging about 7 /". in length, the 

 body tapering off at each end into a delicate flagellum-like extension. 

 It is transmitted directly from one individual to another by intimate 

 contact without the intervention of any intermediate host. It multiplies 

 rapidly and invades all parts of the body including the reproductive 

 cells, or embryo if present in the uterus, so that the offspring when born 

 is already infected. 



The tropical skin disease known as Yaws or " Framboesia tropica " 

 is believed also to be due to a spirochaete {T. perienue, discovered by 

 Castellani) "closely resembling the spirochaete of syphilis. Infection 

 takes place by direct contact, the parasite gaining entrance to the body 

 through any small abrasion or wound of the skin. 



Spirochaetes are by no means restricted in man to the specific diseases 

 that have been mentioned. They are common inhabitants of the mouth 

 and in the septic condition of the gums known as Pyorrhoea alveolaris 

 are found in enormous numbers and in great variety, as may be gathered 

 from Fig. 31. 



Various of the spirochaetes are of very minute size, and in this con- 

 nexion an important observation was made by Schaudinn the discoverer 

 of the parasite of syphilis. He found in the excretory tubes of mosquitos 

 spirochaetes which reproduced so rapidly by fission that the ultimate 



