24 THE BACTERIOPHAGE AND ITS BEHAVIOR 



ULTRAFILTRATION 



I have stated above that the porous candle usually allows the passage 

 of the bacteriophage. When a liquid contains but a very few bac- 

 teriophage corpuscles these may, indeed, be absorbed by the candle 

 and consequently the filtrate becomes ultrasterUe, 



As we will see, the bacteriophage corpuscle, like all ultraviruses, 

 possesses the general properties of colloids. Indeed, this is a charac- 

 teristic of all living things. For a long time the physical chemists have 

 recognized that the porous candle can not be used for the filtration 

 of colloids because of their adsorptive property which causes them 

 to retain the substance fixed to the porous material. 



Even colloids, the micellae of which possess dimensions infinitely 

 smaller than the pores of the candles, may not pass through. As 

 regards ultraviruses we know that for a long time bacteriologists have 

 argued the question of the filtrability of the agents of rabies, of vaccinia, 

 and of variola. And this difference of opinion has been quite legit- 

 imate, for, when filtered through porous candles the passage of the 

 virus is but inconstantly observed. Under these circumstances there 

 is always the possibility that when passage takes place it may have 

 been because of a defective filtering apparatus. But if, instead of 

 the candle an ultrafilter is employed the filtration experiment is in- 

 variably successful, even though the pores are, indeed, very con- 

 siderably smaller. The reason for this is simple. Adsorption, very 

 marked with porcelain, infusorial earth, asbestos, etc., and in general, 

 with all of the mineral substances of which filter candles are com- 

 posed, is reduced to a minimum with the ultrafilter membranes. 

 Theoretically, only ultrafilters should be employed in microbiology. 

 But, as I have said, in working with the bacteriophage, at least for 

 ordinary studies, the convenient filter candle may be used. For special 

 investigations such as seeking for the bacteriophage in body tissues, 

 fluids, or products, it is essential to resort to ultrafiltration. 



Since the matter of ultrafiltration seems to be, in general, rather 

 poorly understood by bacteriologists, it may be well to describe the 

 procedure which is, not only the simplest, but also the most satis- 

 factory in all respects. I have tried all of the methods which have 

 been proposed, and have decided that the method best suited to the 

 work is that of the collodion sac. 



J. C. Martin was the first to apply ultrafiltration, employing a sihca 

 jelly or gelatin. Shortly afterward Roux and Sahmbeni devised the 



