20 GENERAL MORPHOLOGY AND BIOLOGY. 



advance, however, consists in the setting apart among most 

 of the higher bacteria of the free terminations of the filaments 

 for the production of new individuals, as has been described 

 (p. 6). There are various classes under which the species of 

 the higher bacteria are grouped ; but our knowledge of them 

 is still somewhat limited, as many of the members have not 

 yet been artificially cultivated. The beggiatoa group consists 

 of free swimming forms, motile by undulating contractions 

 of their protoplasm. For the demonstration of the rod- 

 like elements of the filaments special staining is necessary. 

 The filaments have no special sheath, and the protoplasm 

 contains sulphur granules. The method of reproduction is 

 doubtful. The thiothrix group resembles the last in structure, 

 and the protoplasm also contains sulphur granules ; but the 

 filaments are attached at one end, and at the other form 

 gonidia. The leptothrix group resembles closely the thio- 

 thrix group, but the protoplasm does not contain sulphur 

 granules. In the dadothrix group there is the appearance 

 of branching, which, however, is of a false kind. What 

 happens is that a terminal cell divides. It divides again, 

 and pushes the product of its first division to 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 belongs 

 the streptothrix actinomyces, or the actinomyces bovis, an 

 important pathogenic agent. Here the organism consists 

 of a felted mass of non- septate filaments, in which true 

 dichotomous branching occurs. Under certain circum- 

 stances 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. Some- 

 times too the protoplasm of the filaments breaks up 

 into bacillus - like elements, which may also have the 



