THE SAPROPHYTIC BACTERIA 107 



The organic materials of which the putrefiable matter is composed 

 are split up step by step. Between the original material and the end- 

 products there will, therefore, be a number of intermediate products. 

 Each intermediate product will, generally speaking, be less complex 

 than the one from which it was produced, and in cases where complete 

 decomposition has taken place, the end-products are simple inorganic 

 elements or compounds. Examples of such end-products are, carbon 

 dioxide, hydrogen, mercaptan sulphuretted hydrogen, etc. Further, 

 as will be presently seen, any one saprophyte does not effect all the 

 changes culminating in the formation of the end-products. In each 

 case of completed decomposition a number, usually a large one, of 

 saprophytes will have taken part, in fact, what we call a piece of 

 decomposing matter is in reality the scene of a hard struggle for 

 existence among different kinds of saprophytes in which first one 

 group, then another, gains the ascendency. The struggle ceases 

 either when the food supply gives out, or when a factor is introduced 

 which is equally inimical to all the organisms. 



In most cases of decomposition the only organisms concerned are the 

 saprophytic bacteria, though under certain circumstances the higher 

 fungi enter into the struggle, as will be presently shown. In this 

 book we shall be able to deal only with the commonest of the sapro- 

 phytic bacteria. Some of them are very abundant in the soil and 

 in the atmosphere, and consequently are practically never absent from 

 decomposing matter. 



The commonest of all is Proteus vulgaris (syn. Bacillus vulgaris, 

 Bacterium vulgare). The morphological characteristics of this organism, 

 and of the group to which it belongs, will be dealt with when we 

 come to consider the sewage-bacteria. 



Several colour-producing saprophytic bacteria are well known, and 

 are widely distributed in nature, the best known being Bac. prodigiosus, 

 Bac. fluarescens liquefaciens, and Bac. pyocyajieum. 



Bac. prodigiosus was responsible for the " Wunderblut " of the Middle 

 Ages. In 1819, for a whole week, blood-red specks appeared on 

 various articles of food at Padua, and in 1848 there was a similar 

 epidemic in Berlin. However, by the latter time, the science of 

 bacteriology, though still in its infancy, had made some strides, so 

 that when the epidemic appeared in Berlin, Ehrenberg, the famous 

 bacteriologist, had no difficulty in clearing up the mystery of the 

 blood-red specks. He showed that each speck was nothing more than 

 a colony of this species. The individuals constituting the organism 

 are short oval rods, 0'5-1'0/x long. Their shortness gives them the 



