8o ZOOLOGY FOR MEDICAL STUDENTS chap. 



series of porcelain filters of graduated degrees of fineness it can be deter- 

 mined that the germs, as indicated by the infectivity of the fluid, pass 

 through the pores of one particular filter of the series while they are 

 stopped by the next. Lastly it has been shown that the transmitting agents 

 of the disease are mosquitos of the genus Stegomyia (p. 250), which if 

 allowed to bite a patient during the first three days of the disease become 

 about twelve days later capable of inoculating the disease into a new 

 individual. Schaudinn's observation then gives a clear hint as to the 

 advisability, in investigating such a disease as Yellow Fever, of bearing 

 in mind that the culprit organism may be a minute spirochaete and that 

 it may be found to lurk in such unexpected nooks in the mosquito's 

 body as the excretory tubes. 



Along with Yellow Fever in this connexion we may bracket Dengue 

 Fever and Pappataci Fever. The former — a widely distributed disease 

 in warm regions — is transmitted by mosquitos, including the species 

 responsible for Yellow Fever. Pappataci or Sand-fly Fever, a common 

 fever in the countries round the Mediterranean, is spread by the small 

 Midge or Sand-fly Phlebotomies. If this fly takes in infected blood from 

 a patient during the first 24 hours of an attack it becomes after an interval 

 of from seven to ten days itself capable of passing on the infection. 



Chlamydozoa 



A number of diseases (e.g. Smallpox, Scarlet Fever, Hydrophobia, 

 Trachoma, Foot and Mouth disease), affecting especially the ectodermal 

 tissues (p. 129) and apparently also due to microbes so minute in size as 

 to pass through ordinary bacterial-filters, are characterized by the 

 presence within the cells of curious rounded inclusions the staining re- 

 actions of which resemble those of achromatic nuclear material. These 

 bodies have been given by pathologists different names in the different 

 diseases in which they have been observed — Guarnieri's bodies. Mallory's 

 bodies, Negri's bodies, Prowazek's bodies and so on — and they have been 

 interpreted as being intracellular parasites of protozoan nature. There 

 is a general tendency now however to regard these bodies not as actual 

 parasites but as being material formed by the host-cell in response to the 

 disturbing effects of parasites. The actual parasites on this view are 

 minute rounded dot-Hke objects which may be observed within the cell- 

 inclusions. That these are living organisms is indicated by their frequently 

 being observed in process of division into two, going through a dumb-bell- 

 shaped stage. As these bodies tend to become enclosed in a sheath (the 

 cell-inclusion) they have been given the name Chlamydozoa and they are 



