158 MICROSCOPIC ANIMAL FORMS AS ANTAGONISTS 



RELATIONS OF PROTOZOA TO FUNGI 



The presence of Colfoda and other infusoria in an active form was 

 found to repress the growth of VerticilUum dahUae in culture media 

 and to prevent infection of tomato plants by this pathogen j Colfoda 

 was also active in soils and reduced the incidence of wilting (88). 



The ability of various fungi to destroy protozoa and nematodes has 

 been studied in detail by Drechsler (194, 195). 



MALARIAL AND TRYPANOSOME PARASITES 



In connection with the recent interest in antibiotic substances, con- 

 siderable work has also been done on the effect of these substances upon 

 different strains of Plasmodium causing malaria and upon different 

 trypanosomes causing various tropical diseases. 



Weinman found (993) that the general correlation between the 

 gram-stain of bacteria and their sensitivity to gramicidin also extends 

 to protozoa (Leishmania, Trypanosoma) and to the Leftosfira tested. 

 Tyrocidine had a marked effect, in concentration of 5 pg/ml., upon 

 the flagellates j they remained active for many hours, gradually losing 

 their motility j a few escaped, giving rise to delayed growth. 



Levaditi and Twort (561) demonstrated that trypanosomes are de- 

 stroyed by B. sub tills and are also partly destroyed by E. coli, but not by 

 B. frodigiosus, B. m^esentericus, B. fyocyaneus. The active substance, 

 designated as trypanotoxin, was found to be produced by B. subtilis in 

 the culture filtrates and in centrifugates. The washed cells of the or- 

 ganism were inactive. The substance is thermolabile and is destroyed at 

 70° C. in 20 minutes. It does not pass collodion dialysis membranes. It 

 is also active in high concentrations against the tic-fever Sfirillum and 

 Leishmania J but not against Borrelia gallinarum. It is apparently not 

 very active in vivo, since it did not protect mice against trypanosomes. 

 Contact between trypanotoxin and trypanosomes in vitro led to the de- 

 velopment of toxo-resistant strains of the latter. This resistance was 

 maintained for many generations j however, the new strains do not be- 

 come more resistant to pyocyanase and other anti-trypanosome re- 

 agents. 



Further studies (560) brought out the following facts: resistant 



