54 Biology of Micro-organisms 



only by its physical effects (heat) or chemic effects (the production of bactericidal 

 substances by electrolysis). 



6. A magnetic field, either within a helix of wire or between the poles of a 

 powerful electromagnet, has no antiseptic or bactericidal effects whatever. 



7. Alternating currents of a 3-inch Ruhmkorff coil passed through bouillon 

 cultures for ten hours favor growth and pigment production. 



8. High-frequency, high potential currents — Tesla currents — have neither 

 antiseptic nor bactericidal properties when passed around a bacterial suspension 

 within a solenoid. When exposed to the brush discharges, ozone is produced 

 and kills the bacteria. 



- 9. Bouillon and hydrocele-fluid cultures in test-tubes of non-resistant forms 

 of bacteria could not be killed by Rontgen rays after forty-eight hours' exposure 

 at a distance of 20 mm. from the tube. 



10. Suspensions of bacteria in agar plates and exposed 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, hypochlor- 

 ous acid, extensive necrosis of the deeper layers of the skin, and phagocytosis. 

 The action of the a:-rays upon bacteria has been investigated by Bonome and 

 Gros,* Pottjt 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 i-rays. 



Movement. — -Rest seems to be the condition best adapted for 

 micro-organismal development. Slow-flowing movements do not 

 have much inhibitory action, 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 interrupted by falls and 

 rapids, should, other things being equal, furnish a better drinking- 

 water than a deep, still-flowing river. 



Galli-ValerioJ has shown, however, that agitation does not in- 

 hibit the growth of the anthrax, typhoid or colon bacilli or the 

 pneumococcus, but sometimes facilitates it. 



Association. — Ssnnbiosis is the vital association of different species 

 of micro-organisms 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 is favored by a 

 change which the staphylococci bring about in the hemoglobin. 



A similar advantageous association has been pointed out by 

 Sanarelli, who found that Bacillus icteroides grows best and retains 



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

 t "Lancet," 1897, vol. 11, No. 21. 



t "Centralbl. f. Bakt.," etc., Sept. 23, 1904, Orig., xxxvii, p. 151. 

 § Socifit^ de Biologic, Sdance du 11 Juin, 1898, "La Semaine medicale," Tune 

 IS, 1898. 



