190 BACTERIA. 



clear liquid to the air, we find in a day or two that it 

 has become cloudy and will begin to give out a disa- 

 greeable odor. Now, if we look at the liquid under a 

 high power microscope we will find it swarming with 

 very minute organisms — some round, like dots or periods 

 in a book, others are rods of varying length and thick- 

 ness, which are straight, and still others are curved, some 

 kinds forming spirals. Many of them are quiet and 

 others are in rapid motion. These are the bacteria, and 

 we call the dot-like form a micrococcus, the straight rod 

 a bacillus and the curved rod a spirillum. This classifi- 

 cation is not a scientific one, but is the most convenient 

 for our purpose. The micrococci are further divided into 

 several groups : when in pairs we call them diplococci ; 

 when in rows, like beads on a string, streptococci ; and 

 when in little clusters, like bunches of grapes, staphylo- 

 cocci. Then there is the tetracoccus in groups of four, 

 and the sarcina in cubical bundles of multiples of four. 

 The organism which causes pneumonia is a diplococcus 

 and it can always be found in the sputum of patients 

 suffering from that disease. This diplococcus is found 

 almost constantly in the saliva of healthy persons, so 

 that it may be said that we carry about with us in our 

 mouths the elements of our own destruction. It is only, 

 however, when the system becomes depressed from some 

 cause that the micro-organism starts its growth, and the 

 disease develops. The sarcinse are found sometimes in 

 large numbers in the fermenting contents of the stomach 

 in cases of chronic dyspepsia and in cancer of the 

 stomach. The bacilli, as I mentioned, are straight rods 

 of varying length and thickness, some so short that they 

 are apt to be confounded with the previous group. The 

 majority of the spirilla are simply curved rods, which 

 sometimes are joined end to end, forming undulatory 

 lines. In some instances they are arranged like a cork- 

 screw and form spirals. A very large one of this sort is 



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