222 STATE BOARD OP AGRICULTURE 



SAPROPHYTIC AND PARASITIC BACTERIA. 



According to habitat, bacteria may be divided into two classes, sapro- 

 phytic, those which live on dead matter; parasitic, those which live on 

 living matter. Among the saprophytic are found the bacteria of the soil, 

 air, and water, and any which do not find their natural conditions when 

 living matter is present. On the other hand, a truly parasitic micro-organ- 

 ism will not live unless associated with life. Nearly all the bacteria pro- 

 ducing infectious diseases are able to live on both living and dead material. 

 There are no fast lines to be drawn in this matter of classification. 



PATHOGENIC AND NON-PATHOGENIC BACTERIA. 



The first of these produce disease by arresting certain functions of the 

 organism or by a change in their tissues. Poisons emanating from this 

 class of micro organisms enter the circulation and give rise to the symtoms 

 manifested in the disease. The non- pathogenic bacteria are unable to 

 develop poisons or institute changes within the animal or plant economy. 



DISTRIBUTION OF BACTERIA. 



^The requirements of bacteria indicate their distribution, for each factor 

 entering into these requirements must determine the existence of bacteria 

 in any geographical location. As an illustration of this, the factor, mois- 

 ture, could be well employed. It has been said that moisture is essential to 

 bacterial growth. Other conditions being suitable, where moisture is, 

 bacterial growth will be abundant, without it, there will be no develop- 

 ment whatever. Put away a piece of leather in a moist cellar, it will con- 

 tract moisture and upon its surface will be noticed certain fungus growths; 

 place it then in a dry atmosphere, the fungus growths will disappear. 

 What explanation can be offered! The light may have some influence, 

 yet leather will mould in light, if moisture is present, but will not mould 

 if there is an absence of moisture. Bacteria act as the moulds. Remove 

 the moisture from a piece of meat and it will keep indefinitely. Fruit is 

 dried that it may keep any length of time; if moisture were to be supplied 

 to that dried fruit, it would decompose within a few hours. Oats in a shock 

 are safe against mould and decay till the rain provides moisture for the 

 latent life that is ready to germinate. Consider for a moment the decom- 

 position that is constantly in process. Organic matter everywhere will 

 decay if moisture is present, take away the moisture and the decomposition 

 will stop. There are certain localities where an animal will dry up, when 

 falling dead, because the moisture is so rapidly evaporated that the 

 bacteria will not have an opportunity to begin their operations of disinte- 

 gration. Not far from this locality the opposite may exist. The animal 

 will fall dead, and the bacteria will soon commence their work of disasso- 

 ciation; not long after the animal will be reduced to the ashes from which 

 it sprang. Moisture, however, is only a factor in the distribution of 

 bacteria and has been used merely to illustrate the importance of single 

 factors in the determination of bacteria any where in nature. The other 

 factors, food, temperature, reaction of media, each in turn could be shown 

 to render a part iu the distribution of bacteria, as important as moisture, 

 but their importance will appear without especial illustration in the body 

 of the discussion. 



