THE MICROBES OF ANIMAL DISEASES. 763 



ease is so common in some districts, in which its spread can not be as- 

 cribed to the bite of flies. Grass, on which the germs of bacteridia 

 had been placed, was given to the sheep. A certain number of them 

 died of splenic fever. The glands and tissues of the back of the throat 

 were very much swelled, as if the inoculation had occurred in the upper 

 part of the alimentary canal, and by means of slight wounds on the 

 surface of the mucous membrane of the mouth. In order to verify the 

 fact, the grass given to the sheep was mixed with thistles and bearded 

 ears of wheat and barley, or other prickly matter, and in consequence 

 the mortality was sensibly increased. 



In cases of spontaneous disease it was surmised that the germs 

 which were artificially introduced into food in the course of these ex- 

 periments are found upon the grass, especially in the neighborhood of 

 places in which infected animals had been buried. It was, in fact, 

 ascertained that these germs existed above and around the infected 

 carcasses, and that they were absent at a certain distance from their 

 burial-place. It is true that putrid fermentation destroys most of the 

 bacteria, but before this occurs a certain number of microbes are dis- 

 persed by the gas disengaged from the carcass ; these dry up and pro- 

 duce germs, which retain their vitality in the soil for a long while. 



The mechanism by means of which these germs are brought to the 

 surface of the soil and on to the grass on which the sheep feed is at 

 once simple and remarkable. Earth-worms prefer soils which are rich 

 in humus or decomposing organic substance, and seek their food round 

 the carcass. They swallow the earth containing the germs of which 

 we have spoken, which they deposit on the surface of the soil, after it 

 has traversed their intestinal canals, in the little heaps with which we 

 are all acquainted. The germs do not lose their virulence in their pas- 

 sage through the worms' intestines, and, if the sheep swallow them 

 together with the grass on which they browse, they may contract the 

 disease. The turning-up of the soil by the spade or plow may produce 

 the same effect. 



A certain warmth is necessary for the formation of germs ; none 

 are produced when it falls below 12, and the carcasses buried in winter 

 are therefore less dangerous than those buried in the spring and sum- 

 mer. It is, in fact, in hot weather that the disease is most prevalent. 

 Animals may, however, contract it even in their stalls from eating dry 

 fodder on which germs of these bacteria remain. 



Pasteur and his pupils performed an experiment in the Jura in 18T9, 

 which clearly shows that the presence of germs above the trenches in 

 which carcasses have been buried is the principal cause of inoculation. 

 Twenty oxen or cows had perished, and several of them were buried 

 in trenches in a meadow where the presence of these germs was ascer- 

 tained. Three of the graves were surrounded by a fence, within which 

 four sheep were placed. Other sheep were folded within a few yards 

 of the former, but in places where no infected animals had been buried. 



