CHAPTER V. 



FUNGI: NON-PATHOGENIC AND PATHOGENIC. 



It is quite outside the scope of the present volume to de- 

 scribe any bacteria other than those giving rise to disease pro- 

 cesses. In the course of his work the bacteriologist frequently 

 meets with ordinary saprophytic organisms. These may occur 

 in diseased organs in which putrefaction has already begun to 

 take place, and they may therefore appear in cultures made 

 from such organs. Their source in cultures may, further, be by 

 contamination from the air, or from the use of insufficiently 

 sterilised vessels or instruments. The positive characters of 

 the pathogenic bacteria will be given, and from these other 

 bacteria must be distinguished by the application of the methods 

 of diagnosis already detailed, or by the special methods still to 

 be described. There occur, however, from time to time as con- 

 taminations of bacterial cultures, organisms of a more compli- 

 cated structure than the bacteria, namely fungi, and therefore 

 we shall describe a few of the typical forms of these. 



The fungi have probably descended from the algas, or both 

 have had a common ancestor. This is shown by the close 

 resemblances in structure and development which the two 

 groups present to each other. The chief differences centre 

 round the degeneration of structure which the adoption of 

 parasitism and saprophytism entails on the fungi. . In the 

 algae, reproduction takes place in both sexual and non-sexual 

 ways. In the former case, certain cells called gametes are set 

 apart, and by the union of two of these — the embryonic male 

 and female elements — a new cell called a zygospore is formed 

 which after a period df rest grows into a new individual. Some- 

 times there is a more definite male element, the antherozoid, and 

 a female element, the oosphere, and the coalescence of these 

 forms an oospore which subsequently behaves like a zygospore. 

 In the non-sexual reproduction there ai'e formed certain cells 



