ORGANISMS WHICH PRODUCE DISEASE 65 



The experimental evidence of the carriage of plague by fleas 

 is extremely interesting. Guinea-pigs and other susceptible 

 animals, if placed in fine gauze- or muslin-protected cages in a 

 plague-infected house or near infected animals, do not catch 

 the infection, whilst similar animals in unprotected cages are 

 infected. Another method by which the caged animals can be 

 protected is to place sticky fly-paper on the ground or platform 

 round the cages for a breadth greater than a flea can jump. 



The organism is a small, somewhat oval-oblong or punt-shaped 

 bacillus, with rounded ends which show characteristic bi-polar 

 staining (see Frontispiece, fig. 11). It is non-motile, does not 

 form spores, and is Gram-negative. It may be found singly or 

 in pairs or even in chains, especially if growing in a fluid. It 

 grows easily in culture best at body-temperature, but also at 

 ordinary room-temperature. It is very resistant to cold, and is 

 not killed by prolonged freezing, but is easily killed by heat and 

 antiseptics. 



Haffkine's Plague Prophylactic Vaccine is prepared from 

 a peptone-broth culture on the surface of which a layer of 

 melted butter or fat is allowed to float. From the under 

 surface of this the organism grows down into the fluid in 

 stalactite-like processes which break off easily on shaking and 

 fall to the bottom. After a sufficient period of growth, the 

 broth culture is killed by heat, standardised, and used in small 

 quantities for injection as a preventive vaccine (see p. 47). 

 Various sera have also been tried for the treatment of plague, 

 but with as yet comparatively little success. 



Several bacilli closely allied to B. pestis produce plague-like 

 diseases in some of the lower animals. 



B. influenzae is a very minute, non-motile, Gram-negative 

 bacillus which is believed by many to be the cause of Influenza 

 in its protean forms. The term " Influenza " is often somewhat 

 loosely used for any highly infectious cold and other ailments, 

 but in the specific disease this bacillus is found, though often 

 along with other pathogenic bacteria, e.g. the Pneumococcus. 

 It may be found in enormous numbers in the discharge from 

 the nose, and in the sputum in bronchitic and pneumonic 

 cases, and it may also be found in the middle ear, the meninges, 

 and elsewhere. 



On culture, it will grow only if haemoglobin, the red colouring 

 matter of the blood, is added to the medium. It forms minute, 

 rounded, transparent colonies, incubation at body temperature 

 being necessary for its growth. It rapidly dies out. It is 

 probably a member of a somewhat large and at present incom- 

 pletely differentiated group of closely related organisms, some 



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