340 



Prof. W. M. Thornton. 



[Jan. 12, 



quantity of electricity passing, but also on the influence of the field, which, 

 though rapidly alternating, may, when high, cause more ionic movement 

 through the cell walls of the organisms, or may act directly by breaking 

 up their protoplasm. 



The voltage gradient used in the later experiments approached unity in 

 electrostatic measure. The force on a charge e (4"6 x 10 -10 E.S.U.) has the 

 same arithmetical value as e in dynes, in unit field. This gives, assuming 

 one such charge upon a section of 3 x 10~ 8 cm. diameter, an average 

 molecular diameter, a stress of 635 grm. per square centimetre, which is 

 enough, when rapidly reversed, to mechanically disintegrate most soft 

 organic tissues, and presumably protoplasm. 



That it is possible to sterilise water by alternating currents at high 

 voltage gradient and current density was shown by exposure for 19 hours at 

 a voltage gradient of 150 per centimetre and a current density of - 3 ampere per 

 square centimetre. One colony developed as compared with a dense growth on 

 the control plate. A comparison of the effects of direct and alternating current 

 when precautions are taken to avoid the influence of electrolytic products 

 shows that they are very similar. The conditions as to length and section 

 of cell and to constant cooling must be observed. 



The results in tap-water were so little different from those in weak salt 

 solutions that the latter may be taken as representative of the degree of 

 sterilisation in tap-water. The effect of time of exposure in the case of 

 B. acidi lactici was examined by comparing plates sown with emulsion after 

 4, 10, and 20 minutes' passage of the current through it, with a control plate. 

 The numbers of colonies are respectively 8000, 300, and 20, the growth in 

 the control entirely covering the agar. This organism is therefore more 

 sensitive to the current than B. coli communis. Later results with older 

 cultures do not show so marked a difference, though it is always similar. 

 The chief interest of this lies in the fact that with a current density of 

 - 5 ampere per square centimetre in cold water, 20 minutes does not cause 

 complete sterilisation, whereas with new milk a shorter exposure does so. 

 One reason for this, apart from heating and cooling, may be that in the latter 

 case the bacteria were just beginning to grow, and were therefore more 

 sensitive to the influence of the current. 



6. The Sterilisation of Milk by Alternating Current. 

 For the purpose of exposing milk to alternating currents two large 

 platinum crucibles were arranged, one inside the other, to form a cell, the 

 distance between them at the bottom being - 7 cm. The interspace could 

 be filled through a hole in the ebonite cap with a known quantity of liquid. 



