DESICCATION 111 



pletely sterile at the end of an hour, but filtrates showed the presence of the typhoid Vi 

 antigen and the streptococcal labile antigen respectively. Rivers, Smadel and Chambers 

 (1937) were successful in bringing about a considerable degree of destruction of vaccinia 

 virus in the form of washed elementary bodies, but not in ordinary tissue suspensions. 

 The presence of protein in the suspension interferes with the effect of the waves ; this 

 may explain why attempts to destroy bacteria in milk, bacteriophage in cultures, and 

 viruses in tissue suspensions have often proved a failure (Beckwith and Weaver 1936, 

 Scherp and Chambers 1936). 



Supersonic waves, i.e. waves above audible frequency, of 200,000 to 1,500,000 

 cycles per second, produced by connecting a piezo-electric crystal with a high- 

 frequency oscillator, are also credited with bactericidal power. The observations 

 of Beckwith and Olson (1932), Yen and Liu (1934), and Takahashi and Christensen 

 (1934) suggest that a considerable destruction of bacteria, and even of filtrable 

 viruses, may be brought about by exposure to these waves for an hour or so. 

 Paic and his colleagues (1935fl, h), however, found tbat ultrasonic waves of a 

 frequency of 280,000 cycles per second had no destructive action in 2 hours on 

 certain toxins, a coli bacteriophage, the herpes virus, or a number of different 

 micro-organisms, while completely sterilizing a culture of Paramoecmm in 5 

 minutes. 



Too little work has yet been carried out to justify a critical discussion of the 

 results. It is generally believed that the action of the waves, which are of course 

 molecular and not electro-magnetic, is due to the disruption of the cell as a result 

 of the violent agitation set up in its contents. According to Liu and Yen (1934) 

 no effect is produced on cells exposed in vacuo, suggesting that cavitation of dis- 

 solved gases plays an important part in the disruption of the bacteria. Probably 

 a relationship exists between the wave length and the size of the organism or 

 molecule exposed. Against the simple disruption explanation may be set the 

 observations of Rivers, Smadel and Chambers (1937) on the effect of sonic waves 

 on washed vaccine virus. Though the infective titre of the suspension fell from 

 10~^ to less than 10""^, no microscopical evidence of disintegration of the elementary 

 bodies could be obtained, nor was there any increase in the opacity of the suspension. 

 The authors, therefore, suggest that the destructive effect may be due to the forma- 

 tion of some oxidizing substance from the water. 



Desiccation. — If dried on silk threads or glass slips, the proportion of organisms 

 surviving for any given length of time varies with a great number of factors, such 

 as the species of bacterium, the initial numbers present, the nature of the suspend- 

 ing medium, the rapidity of drying, and the temperature and gaseous nature of 

 the environment (see Ficker 1898). Anthrax spores dried on silk threads may 

 survive for over 20 years, while many of the pathogenic non-sporing bacteria 

 die in a few hours. Paid, Birstein, and Reusz (1910a), working with staphylococci 

 dried on garnets, found that the velocity of disinfection was equal to the square 

 root of the oxygen concentration. The lower the temperature at which the 

 organisms were kept after being dried in this way, the smaller was the proportion 

 that succumbed (Paul 1909). 



More recent work (see Often 1930, 1932, Elser, Thomas, and Steffen 1935, 

 Flosdorf and Mudd 1935) has shown that even non-sporing pathogenic organisms 

 are able to survive drying indefinitely, provided that desiccation is complete and 

 that the dried organisms are maintained in a high vacuum (0-01 mm. Hg or less). 

 Even such sensitive organisms as the meningococcus and the gonococcus remain 



