44 Biology of Bacteria 



for four hours to the rays, according to Rieder's plan, were 

 not killed. 



11. Tubercular sputum exposed to the Rontgen rays for 

 six hours, at a distance of 20 mm. from the tube, caused 

 acute miliary tuberculosis of all the guinea-pigs inoculated 

 with it. 



12. Rontgen rays have no direct bactericidal properties. 

 The clinical results must be explained by other factors, 

 possibly the production of ozone, hypochlorous acid, ex- 

 tensive necrosis of the deeper layers of the skin, and phago- 

 cytosis. The action of the x-rays upon bacteria has been 

 investigated by Bonome and Gros,* Pott,t and others. 

 When the cultures are exposed to their action for prolonged 

 periods, their vitality and virulence seem to be slightly 

 diminished. They are not killed by the x-rays. 



Movement. Rest seems to be the condition best adapted 

 for micro-organismal development. Slow-flowing movements 

 do not have much inhibitory action upon the growth of 

 bacteria, but violent agitation, as by shaking a culture 

 in a machine, may hinder or prevent it. This explains 

 why rapidly flowing streams, whose currents are inter- 

 rupted by falls and rapids, should, other things being equal, 

 furnish a better drinking-water than a deep, still-flowing 

 river. 



Galli-Valerio { has shown, however, that agitation does 

 not inhibit the growth of the anthrax, typhoid or colon 

 bacilli or the pneumococcus, but sometimes facilitates it. 



Association. Symbiosis is the vital association of dif- 

 ferent species of bacteria by which mutual benefit to one 

 or the other is brought about. Antibiosis is an association 

 detrimental to one of the associated organisms. Bacterial 

 growth is greatly modified by the association of different 

 species. Coley found the streptococcus more active when 

 combined with Bacillus prodigiosus ; Pawlowski that mixed 

 cultures of Bacillus anthracis and Bacillus prodigiosus were 

 less virulent than pure cultures of anthrax ; Meunier that 

 when the influenza bacillus of Pfeiffer is inoculated upon 

 blood agar together with Staphylococcus aureus its growth 



* " Giornal. med. del Regis Esercito, " an 45, u. 6. 



t " Lancet," vol. n, No. 21, 1897. 



J " Central bl. f. Bakt.," etc., I Orig. 4, xxxvn, Sept. 23, 1904, 

 p. 151. 



Societe de Biologic, Seance du n Juin, 1898; "La Semaine medi- 

 cale," June 15, 1898. 



