CONTAGIUM. 81 



and whether motile or not. There are at least three general fam- 

 ily types of bacteria : Coccaceae, Bacteriaceae, and Spirillaceae. 

 lwo of these general groups (coccaceae, and bacteriaceae) con- 

 tain most of the species that are known to cause diseases of do- 

 mestic animals. 



First, Coccaceae. — These are spherical. They multiply in 

 from one to three different planes and are grouped accordingly 

 in chains ; in masses extending in two directions ; and in masses 

 extending in three directions. Under the microscope these little 

 germs appear as round dots. A great many of the most com- 

 mon diseases are caused by germs which belong to this general 

 family. For instance, erysipelas and various types of blood pois- 

 oning, abscesses and sloughing. 



Second, Bacteriaceae. — These are short rod-shaped germs, 

 and include two especially important genera, Bacillus and Bac- 

 terium. Among the common diseases of live stock, which are 

 caused by germs belonging to this general family, there may be 

 given as illustrations tuberculosis, hog cholera, swine plague, 

 glanders, tetanus (lock jaw, and haemorrhagic septicaemia. 



Third, Spirillaceae. — This group is not especially important 

 in veterinary medicine. The individuals are rod shaped, curved 

 or spiril and may be very short or very long. The specific cause 

 ■of Asiatic fever (human) belongs in this general group. 



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