226 HEALTH AND DISEASE 



Pasteur, Bunion Sanderson, Duguid, and others, that the rod-like body, 

 bacillus anthracis, was accepted as the true cause of anthrax; and the 

 demonstration of this important fact may be looked upon as the founda- 

 tion of the doctrine of contagium vivum, as the origin of contagious 

 disease. 



Morphology of bacteria. — Bacteria have been defined as minute 

 vegetable cells. Their claim to a vegetable origin is based upon the ex- 

 perimental fact that they have the power of obtaining their nitrogen from 

 ammonia, a property which is not possessed by animals. In form these 

 organisms vary considerably: the most primitive is to be found in the 

 extremely minute round or oval cells which are described as cocci (fig. 74), 



Fig. 74. —Bacteria and Bacilli. Highly magnified 



it, Cocci, singly and varying in size. b, Cocci in chains (streptococcus). c. Cocci in masses (st<i/iln/locaccus). 

 t and e, ( iooci in pairs [diplococcKs), f, Cocci in groups of four (meriimopedia). g, I loooi in packets [sarcina). h, Bac- 

 Cerium [Septicaemia huemorrhagicoe). i, Bacillus (B.subtilis). Tc, Spore formation illustrated by Bacillus anthraeu. 



the variation in size being indicated by the prefix mega for the larger and 

 micro for the smaller cocci, hence the terms megacocci and micrococci. 

 When two circular or oval cells are joined together they are described 

 as diplococci. When a number of cells are united to form a chain, the 

 organism is termed streptococcus. When there is a combination of four 

 cocci the term tetrad, or merismopedia, is applied. When the packet 

 consists of eight divisions a sarcinacoccus is formed. When irregular 

 heaps like bunches of grapes are found, the mass is called staphylococcus, 

 and if irregular masses of cocci are found imbedded in a gelatinous matrix 

 it is called ascococcus. Some micro-organisms present a rod-like character, 

 varying considerably in length; the very short rods with rounded ends 

 are described as bacteria, the longer ones as bacilli, which term is always 



