Experiments with Contagious Diseases of Animals 

 and Insects of Europe. 



Mr. Jean Danysz, of the Pasteur Institute, has given a detailed account * 

 of recent experiments for the transmission of contagious diseases among 

 noxious animals and insects. As his methods and conclusions are of im- 

 mediate interest to American farmers, it is thought best to embody herein a 

 resume 1 of his report. 



When insects and rodents appear in great numbers they succumb to con- 

 tagious diseases, but unfortunately these epidemics come spontaneously only 

 after the crops have been destroyed. Many experiments tried in recent 

 years have shown that rodents can be artificially infected with great suc- 

 cess. Field mice are the most numerous of European and American ani- 

 mals. Of the several species of field mice, Arvicola agrestis or arvalis and 

 A. subterraneous are the most widespread and dangerous to crops. They 

 appear suddenly towards the end of summer in legions, attacking forage 

 plants, cereals, vines, and young trees. Nine great invasions of these field 

 mice have been noted in France from 1822 to 1892. These animals were 

 formerly thought to be migratory, but late researches have shown that all 

 are born near where they are found, sometimes spreading to adjoining fields 

 only. The intensity and rapidity of their invasion is due to incredible 

 fecundity and the preponderance of the females. The progeny of a single 

 pair may number 350 individuals in a year. When the number becomes 

 extremely great in a given locality they lack for food and become an easy 

 prey to disease. Epidemics occur spontaneously, and so nature herself fur- 

 nishes means for destroying these pests, but not at the right lime. To turn 

 these artificial diseases to advantage it is necessary to regulate them, to 

 choose one that is injurious only to rodents and not to farm animals, and 

 to create centers of infection at a time most favorable for preventing in- 

 vasions. 



A microbe found on a field mouse killed by an epidemic in Seine-et-Marne 

 is a bacillus. It develops rapidly in all known artificial nutritive media. 

 It presents very dissimilar features according to the media and the condi- 

 tions of culture. It has been found to be virulent for all species of moles, 

 domestic mice, wood and garden mice and black rats in France. Its action 

 on big gray rats is less apparent. It is always fatal and extremely conta- 

 gious. At an autopsy, there is generally found hypertrophy of the spleen, 



* Maladies Contagieuses des Animaux Nusibles leurs Applications en Agriculture, in Annals de la 

 Science Agrononiique, 1895, page 1. 



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