20 GENERAL MORPHOLOGY AND BIOLOGY. 



like bodies from which new individuals can be repro- 

 duced. Such bodies are often referred to as spores, but 

 they have not the same staining reactions nor resisting 

 powers of so high a degree as ordinary bacterial spores. 

 Sometimes also the protoplasm of the filaments breaks 

 up into bacillus -like elements, which may also have the 

 capacity of originating new individuals. In the strepto- 

 thrix actinomyces there may appear a club-shaped swelling 

 of the membrane at the end of the filament, which has by 

 some been looked on as a spore formation, but which is 

 most probably a product of a degenerative change. The 

 streptothrix group as a whole is a link between the bacteria 

 on the one hand, and the lower fungi on the other. Like 

 the latter, the streptothrix forms show the felted mass of 

 non-septate branching filaments, which is usually called a 

 mycelium. On the other hand, the breaking up of the 

 protoplasm of the streptothrix into coccus- and bacillus-like 

 forms, links it to the other bacteria. 



GENERAL BIOLOGY OF THE BACTERIA. 



There are five prime factors which must be considered 

 in the growth of bacteria, namely, food supply, moisture, 

 relation to gaseous environment, temperature, and light. 



Food Supply. The great function performed by bacteria 

 in nature is the breaking up into simpler constituents of 

 the complicated organic substances which form the bodies 

 of dead plants and animals, or which are excreted by the 

 latter while they are yet alive. The natural food of bacteria 

 is therefore of an extremely complex nature. Not only 

 is it so to start with, but seeing that, to speak generally, 

 many bacteria grow side by side, the food supply of any 

 particular variety of the latter is, relatively to it, altered 

 by the growth of the other varieties present. It is thus 

 impossible to imitate the natural food environment of any 

 species. The artificial media used in bacteriological work 

 may therefore be poor substitutes for the natural supply. 

 In certain cases, however, the conditions under which we 



