192 General Biology 



they are called staphylococci ( ) ; and if in three, 



sarcina ( ). (Fig. 89.) 



Sometimes the protoplasm of bacteria breaks up into a number of 

 bodies within the cell. These bodies are called endospores ( ). 



The value of this breaking up is supposed to be similar to that of 

 encysted amoeba ; namely, to permit the organisms to await some more 

 favorable feeding period and environment. During this spore state 

 bacteria are very resistant. 



The sterilization of various substances in the laboratory takes 

 sporulation into consideration, so that when a substance is to be steril- 

 ized, it is placed in a temperature of 50 or 60 degrees C. for several days 

 in succession, rather than at a higher temperature at one time. This 

 permits the spores to germinate. As spores are hard to kill while in 

 the spore-state, but readily succumb when placed in a 50 or 60 degrees 

 C. temperature after germination, it will be seen that this intermittent 

 sterilization is the best method so far known. 



Fischer has divided bacteria into three groups, according to the 

 nature of their metabolism: "(1) Bacteria which are like the green 

 plants in requiring neither organic carbon nor organic nitrogen. These 

 are the so-called prototrophic bacteria, which possess the remarkable 

 property of being able to build up both carbohydrates and protein out 

 of carbon dioxide and inorganic salts. (2) Bacteria which need organic 

 carbon and nitrogenous compounds. These are called the metatrophic 

 bacteria. (3) The paratrophic bacteria which live as true parasites and 

 can exist only within the living tissue. This group cannot manufacture 

 its own food and is like other animals in this respect. The metabolism 

 of bacteria may then show all of the phases already described for green 

 plant cells and for animal cells as well as certain additional phases. 

 The food is absorbed directly through the cell wall and is as varied as 

 is their habitat. There seems to be no form of organic substance living 

 or dead that may not serve as a source of food supply for bacteria, so 

 that the enumeration of their foods becomes practically impossible. A 

 special phase of the metabolism of bacteria is illustrated in their relation 

 to nitrogen compounds. Nitrogen in an uncombined state cannot be 

 used as food energy by most plants. It is obvious that the amount of 

 ammonia, nitrites, and nitrates would soon become exhausted unless 

 there were some way of supplying more of the nitrogen compounds. 

 Many of the soil bacteria are prototrophic in habit and carry on the 

 important work of combining the free nitrogen into a form that can be 

 used by other organisms. The several nitrogen combinations are effected 

 through the agency of several kinds of bacteria. There are also bacteria 

 which live in the roots of certain plants, like clover, beans, and peas, 

 which are able to utilize the nitrogen of the air. All of the higher forms 

 of plants and all of the animals are dependent upon microscopic bacteria 

 for their nitrogen. It would be very strange if the character of meta- 

 bolism which is so fundamental in living things should be essentially 



