5° 



PATHOGENIC BACTERIA. 



teria will destroy them. Carbolic acid and biclilorid of 

 mercury are the best known examples. 



It is interesting to mention in this connection the 

 results of the experiments of Trambusti, who found it 

 possible to produce a tolerance to a certain amount of 

 bichlorid of mercury by cultivating Friedlander's bacil- 

 lus upon culture-media containing gradually increasing 

 amounts of the salt, until from 1-15,000, which inhibited 

 ordinary cultures, it could accommodate itself to 1-2000. 



Variations in the amount of oxygen, temperature, moist- 

 ure, etc., beyond what have been described, are prej- 

 udicial to the growth and development of bacteria, first 

 inhibiting their growth, thus tending toward their de- 

 struction. In the practical application of our knowledge 

 of the biology of the bacteria we constantly make use of 

 such precautions as removing from surgical dressings, 

 sponges, etc., every substance that can possibly afford 

 nutriment to bacteria, and heating such materials, as well 

 as culture-media and a variety of other substances, to a 

 temperature beyond that known to be the extreme limit 

 of bacterial endurance. 



Some forms of the bacteria are never found except in 

 the tissues of diseased animals. Such organisms are 

 •called parasites. The parasitic group really is divisible 

 into the purely parasitic and the occasionally parasitic 

 bacteria. Of the first division the tubercle bacillus may 

 be used as an illustration, for, so far as is known, it is 

 never found in other places than the bodies and dejecta 

 of diseased animals. The cholera spirillum illustrates 

 the second group, for, while it produces the disease 

 known as Asiatic cholera when admitted to the digestive 

 tract, it is a constant inhabitant of certain waters, where 

 it multiplies with luxuriance. 



Bacteria which do not enter the animal economy, or if 

 accidentally admitted do no harm, but live upon decaying 

 animal and vegetable materials, are called saprophytes. 



According to their products of metabolism, bacteria 

 are often described as — 



