CHAPTER XXXVI. 



LOWER HYPHOMYCETES TRICHOMYCETESLEPTOTHRIX 

 CLADOTHRIX STREPTOTHRIX AND ACTINOMYCES. 



HYPHOMYCETES. 



THE organisms discussed in the preceding pages have been con- 

 sidered chiefly from the point of view of being the cause or etiologic 

 factor of disease in domestic animals and man. All of them are 

 exceedingly simple, unicellular, vegetable microbes, and they are 

 known as bacteria or schizomycetes. The term schizomycetes denotes 

 fission fungi and is descriptive of the characteristic mode of binary 

 division or fission common to all organisms belonging to the bacteria. 

 True branching 1 does not occur among the latter, while the higher 

 fungi, eumycetes or hyphomycetes, do form genuine branches. For 

 this reason they may be defined as vegetable microorganisms composed 

 of elongated or filiform cells, which form genuine branches and which 

 multiply by special organs or cells called spores. Their development 

 is characterized by the formation of true branches from the original 

 cell or main trunk, and the latter and the branches form one con- 

 tinuous mass of protoplasm. The branching may be a comparatively 

 simple arrangement as in the lower eumycetes, or it may be relatively 

 complicated with a vast network of dichotomous and pseudodicho- 

 tomous divisions as in the higher eumycetes. The term true dicho- 

 tomous division designates a division into two equal branches, while 

 pseudodichotomous division indicates that one branch, which is 

 continued as the principal stem, sends out a lateral, often smaller 

 branch. 



When the hyphomycetes or, as they are commonly called, the 

 moulds are studied a differentiation of the organism into two parts 

 which perform different physiologic functions can be distinguished. 

 One part, the mycelium, presents itself as a more or less branched 

 mass which serves for the nutrition and preservation of the individual 

 organism, while the second part, known as the fructification organ, 

 produces the spores and serves for the preservation of the species. 

 The entire soft cellular structure, without any wooden fibers, of which 

 the whole body of the mould consists, is known as the thallus. 



1 Bacteria like the tubercle bacillus are not taken into consideration at this place, notwith- 

 standing the fact that this organism sometimes forms true branches, indicating, perhaps, 

 that it should be classified among the lower eumycetes rather than among the bacteria. Since 

 such organisms have always been classified among the bacteria in medical considerations, it 

 is not desirable to make any change. 



