12 BACTERIOLOGY 



number the majority of the organisms studied in Bacteriology. 

 It is subdivided as follows : 



1. Euphyceae or true Algae : these vary from the simple, 

 thread-like and microscopic forms found in ponds and stagnant 

 pools and in moist places, up to the more, and sometimes highly, 

 complex, forms such as the seaweeds, some of which may be 

 several hundred feet long. They are all characterised by the 

 presence of chlorophyll, the green substance by which plants, 

 under the influence of sunlight, can absorb their food and build 

 it up into more complex substances, and are thus differentiated 

 from the fungi, which some authorities regard as modified algae 

 which have lost their chlorophyll. The resemblance of some 

 of these to bacteria is merely superficial. Though none of this 

 group are known to cause definite disease in man, their growth 

 in reservoirs and cisterns may cause deterioration of water- 

 supplies, and they may even sometimes be seen as a green 

 sediment in water-vessels that are not properly cleaned out. 



2. Eumycetes or True Fungi : such as toadstools and mush- 

 rooms, mildews, moulds, etc. These consist of threadlike 

 structures (hyphae) often forming a network or tangled mass 

 which is known as the mycelium. From these, under suitable 

 conditions, are developed fruit-bearing structures or fructifi- 

 cations, some of which are familiar to us as toadstools or as the 

 velvet-like pile of the moulds the mycelial threads or fungus 

 proper being underground, or in the substance of the material 

 (cheese, jam, etc.) on which the organism is growing and from 

 which it derives its nourishment. 



3. Saccharomycetes or Yeasts : a group coming intermediate 

 between the moulds and the bacteria, are important both in 

 relation to various fermentation-processes and, in less degree, 

 as producers of disease. 



4. Diatomaceae : closely allied to the Algae, but possessing 

 a flinty skeleton, sometimes of great beauty. They are founcj 

 in water and moist places ; and fossil deposits of their skeletons 

 constitute the so-called " infusorial earth " used in the manu- 

 facture of dynamite and certain kinds of paint. They are not 

 known to produce disease, but are of great interest to the 

 geologist, vast deposits of them being often found in ocean- 

 beds and in rock and other strata originally formed at the 

 bottom of the ocean. 



5. Myxomycetes or Slime-Moulds : some writers have 

 classed these in the animal kingdom. They grow upon moist 

 decaying organic matter, and their methods of reproduction are 

 more complex than those of bacteria. They are not of special 

 importance from our present point of view. 



6. Myxobacteriaceae : also found growing on moist decay- 



