!4 BIOLOGICAL LECTURES. 



pneumonia under any circumstances, and domestic animals 

 never contract yellow fever or cholera during the epidemic 

 prevalence of these diseases. 



The relative immunity, natural or acquired, to diseases which 

 are not strictly limited to a single species, may often be over- 

 come by various agencies acting upon the individual exposed 

 to infection. Thus Arloing was able to induce symptomatic 

 anthrax in animals naturally immune for this disease by mix- 

 ing with his cultures various chemical substances, such as car- 

 bolic acid, pyrogallic acid, and especially lactic acid (twenty 

 per cent). Leo has shown that white mice, which are not 

 subject to the pathogenic action of the glanders bacillus, may 

 be rendered susceptible by feeding them for some time upon 

 phloridzin, which gives rise to an artificial diabetes, and causes 

 the tissues to become impregnated with sugar. Behring 

 claims to have demonstrated by experiment that white rats 

 lose their immunity for anthrax when fed for some time upon 

 an exclusively vegetable diet, or when phosphate of lime is 

 added to their food ; and he has suggested that the immunity 

 of these animals may be due to the highly alkaline reaction of 

 their blood and tissue juices. Nocard and Roux found by 

 experiment that an attenuated culture of the anthrax bacillus, 

 which was not fatal to guinea pigs, killed these animals when 

 injected into the muscles of the thigh after they had been 

 bruised by mechanical violence. Abarrin and Roger found 

 that white rats, which are not susceptible to anthrax, became 

 infected and frequently died if they were exhausted, previous 

 to inoculation, by being compelled to turn a revolving wheel 

 for a considerable time. Pasteur found that fowls, which have 

 a natural immunity against anthrax, become infected and perish 

 if they are subjected to artificial refrigeration after inoculation. 

 This has been confirmed by the more recent experiments of 

 Wagner (1891). According to Canalis and Morpurgo, pigeons 

 which are enfeebled by inanition easily contract anthrax as 

 a result of inoculation. Arloing states that sheep which have 

 been freely bled contract anthrax more easily than others ; and 

 Serafini found that when dogs were freely bled, the bacillus of 

 Friedlander, injected into the trachea or the pleural cavity, 



