164 Messrs. H. G. Thornton and G. Smith. 



unable to thrive. This is the result of the holozoic mode of nutrition of the 

 flagellates, which feed greedily on the bacteria in the culture and are always 

 to be found in greatest abundance in the bacterial scum at the surface. 



The development of the soil flagellates in the culture is evidently 

 dependent upon the bacterial flora in the tube. In the tyrosin media the 

 bacterial growth reaches its most favourable degree for the development of 

 the flagellates. In the case of cultures in media containing alanine it is 

 frequently found that the flagellates fail to attain their maximum growth, 

 being probably swamped by the excessive numbers of bacteria. 



In order to discover whether the Miquel salts were necessary for the 

 growth of the soil flagellates, a culture medium was made up by adding solid 

 tyrosin to 10 c.c. of tap-water, and this was inoculated with a strong culture 

 of Prowazekia terricola. This culture entirely failed to develop, remaining 

 almost entirely free even of bacteria, which were evidently unable to develop 

 satisfactorily in the absence of the salts of the Miquel solution. 



The Prowazekia were observed to flourish in cultures containing very 

 varied types of bacteria. In order to discover whether the flagellates 

 exercised any selective faculty when feeding upon the bacteria, a number of 

 smear preparations were made from different cultures. The films were fixed 

 with corrosive acetic or with osmic vapour, and were stained with iron 

 hsematoxylin. These preparations showed that bacteria of all the types 

 surrounding tire flagellates were ingested in quite a promiscuous manner (see 

 Plate 12). 



The cultures inoculated with various soils, both in the test-tubes and in 

 drop cultures which were also made, show the enormous abundance and wide 

 distribution of these minute flagellates as compared with other soil protozoa. 



Although ciliates and amoeba? often fail to appear in tubes inoculated with 

 a very small quantity of soil, yet all the types of soil that have been tried 

 have yielded at least some Prowazekia when inoculated into the appropriate 

 culture media. The organism has also been found in tap water and in water 

 from an open-air tank. 



The very rapid increase of these minute flagellates is also very noticeable. 

 Under the optimum culture conditions it has been found possible to obtain 

 a strong growth of the flagellates within 48 hours of the time of inoculation. 

 On the other hand the larger protozoa, such as the ciliates, do not become 

 even noticeable in the tubes until a week or so has elapsed. 



The great abundance and wide distribution of the minute flagellates, taken 

 in conjunction with their rapid powers of increase, suggest that in all 

 probability they are of much greater importance than the larger soil protozoa 

 as a factor in the destruction of soil bacteria. 



