SIZE, SHAPE, AND HYDRATION OF VIRUSES 



23 



viscosity rj flowing in a time t under a pressure difference P is 

 given by 



,. TT IP ^ 



8 rj I 



(2.1) 



Everything can be measured as far as this expression is con- 

 cerned except r^ and n, so that we can consider a rate-of-flow 



Fig. 2.3. Illustrating the principle of calibrating a collodion filter. 



experiment as determining ?ir'^. By measuring the volume, v, of 

 Hquid absorbed and held by the filter, we have 



V = n TTT^ I 



The thickness, I, is then directly measured, and we have 



V 



vPrH 



(2.2) 



(2.3) 



from which r can be found. 



Markham, Smith, and Lea (1942) have subjected this to 

 considerable examination. They conclude, from calibrations 

 made with vaccinia, bushy stunt, hemocyanin, and hemoglobin, 

 that the ratio of size of particle to average pore diameter is 

 between 0.55 and 0.95, indicating, therefore, rather large limits 

 of error. Stanley and Lauffer (1948) point out that as the par- 

 ticles and pore sizes both increase, the ratio approaches nearer 

 to unity. Table 2.1 gives some comparative values. The units 

 used are Angstrom units. 



A very good idea of the ultrafiltration method can be gained 

 from the work of Melnick, Rhian, Warren, and Breeze (1951) 

 who have applied it to Coxsackie virus and Lansing polio virus 



