FOOD SUPPLY 17 



one side. There are thus two terminal cells lying side by side, 

 and as each goes on dividing, the appearance of branching is 

 given. Here, again, there is gonidium formation; and while 

 the parent organism is in some of its elements motile, the gonidia 

 move by means of flagella. The highest development is in the 

 streptothrix group, to which belong the streptothrix actinomyces, 

 or the actinomyces bovis, and several other important pathogenic 

 agents. Here the organism consists of a felted mass of non- 

 septate filaments, in which true dichotomous branching occurs. 

 Under certain circumstances threads grow out, and produce 

 chains of coccus-like bodies from which new individuals can be 

 reproduced. 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, too, 

 the protoplasm of the filaments breaks up into bacillus-like 

 elements, which may also have the capacity of originating new 

 individuals. In the streptothrix 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 an organ 

 of fructification, but which is most probably a product of a 

 degenerative change. The streptothrix group, though its 

 morphology and relationships are much disputed, may be looked 

 on as 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 in the growth of bacteria which 

 must be considered, namely, food supply, moisture, relation to 

 gaseous environment, temperature, and light. 



Food Supply. The bacteria are chiefly found living on 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. Seeing that, as a general rule, many bacteria 

 grow side by side, the food supply of any particular variety is, 

 relatively to it, altered by the growth of the other varieties 

 present. It is thus impossible to imitate the complexity of 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 



