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386 BACTERIA PATHOGENIC TO MAN 



Spore formation, as already noted, only takes place in the pres- 

 ence of oxygen, and at a temperature of 15 to 43 C. There is no 

 development of spores at a greater depth than 1.5 metres in the earth, 

 or in the bodies of living or dead animals; but spores may be found 

 in the fluids containing the bacilli when these come in contact with 

 the air, as in bloody discharges from the nostrils or from the bowels 

 of the dead animal. 



There are certain non-spore bearing species of anthrax. Sporeless 

 varieties have also been produced artificially by cultivating the typical 

 anthrax bacillus under unfavorable conditions, among which may 

 be mentioned the addition of antiseptics, as carbolic acid. Varieties 

 differing in their pathogenic power may also be produced artificially. 

 Pasteur produced an "attenuated virus" by keeping his cultures for a 

 considerable time before replanting them upon fresh soil. 



Anthrax cultures containing spores retain their vitality for years; 

 in the absence of spores the vitality is much more rapidly lost. When 

 grown in liquids rich in albumin the bacilli attain a considerable degree 

 of resistance; thus dried anthrax blood has been found to retain its 

 virulence for sixty days, while dried bouillon cultures only did so for 

 twenty-one days. Dried anthrax spores may be preserved for many 

 years without losing their vitality or virulence. They also resist a 

 'I comparatively high temperature. Exposed in dry air they require a 

 temperature of 140 C. maintained for three hours to destroy them; 

 but suspended in a liquid they are destroyed in four minutes by a tem- 

 perature of 100 C. 



Pathogenesis. The anthrax bacillus is pathogenic for cattle, sheep, 

 (except the Algerian race), horses, swine, mice, guinea-pigs, and rabbits. 

 Rats, cats, dogs, chickens, owls, pigeons, and frogs are but little sus- 

 ceptible to infection. Small birds the sparrow particularly are 

 somewhat susceptible. Man, though subject to local infection and 

 occasionally to internal forms of the disease, is not as susceptible as 

 some of the lower animals. 



In susceptible animals the anthrax bacillus produces a true septi- 

 caemia. Among test animals mice are the most susceptible, succumb- 

 ing to very minute injections of a slightly virulent virus; next guinea- 

 pigs, and lastly rabbits, both of these animals dying after inoculation 

 with virulent bacilli. Infection is most promptly produced by intro- 

 duction of the bacilli into the circulation or the tissues, but inocu- 

 lation by contact with wounds on the skin also causes infection. It is 

 difficult to produce infection by the ingestion even of spores; but it 

 may readily be caused by inhalation, particularly of spores. 



Subcutaneous injections of these susceptible animals results in 

 ^ath in from one to three days. Comparatively little local reaction 

 occurs immediately at the point of inoculation, but beyond this there 

 is an extensive oedema of the tissues. Very few bacilli are found in 

 the blood in the larger vessels, but in the internal organs, and especially 

 in the capillaries of the liver, the kidneys, and the lungs, they are present 

 in great numbers. In some places, as in the glomeruli of the kidneys, 



