INTERMEDIATE ORGANISMS 191 



planes 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 bac- 

 teria are very resistant. 



The sterilization of various substances in the laboratory takes spor- 

 ulation into consideration, so that when a substance is to be sterilized, 

 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 per- 

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

 spore-state, but readily succumb when placed in a 50 to 60 degrees C. 

 temperature after germination, it w r ill be seen that this intermittent 

 sterilization is the best method so far known. 



"Fischer divided bacteria into three groups, according to the na- 

 ture 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 bac- 

 teria 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 am- 

 monia, 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- 



