NATURE OF BACTERIOPHAGE 337 



As Maitland very logically states, if the increase in the bacterio- 

 phage principle were the result of the metabolism of the bacterium, just 

 as soon as one obtains an increase of a single principle at the expense of 

 bacteria belonging to different species, the characters of the principle 

 should differ to accord with the regeneration, depending upon whether 

 it takes place with one bacterium or with another. But expermient 

 shows that quite the opposite occurs, that the bacteriophage remains 

 endowed with the same properties. Consequently Maitland has con- 

 cluded that the bacteriophage is not a bacterial product, but that it is 

 foreign to the bacterium. 



VI. Asheshov^" isolated from the intestinal contents of a pig two 

 different races of the bacteriophage, both active for B. dysenteriae 

 Flexner. Upon agar, one formed very large plaques, 12 to 15 mm. in 

 diameter, the other produced only very minute plaques, from 1 to 2 

 mm. He carried out two parallel series of passages at the expense of a 

 single strain of the Flexner bacillus, the suspensions for each passage 

 with the two races being prepared from the same agar culture. After a 

 series of 15 passages, each of the bacteriophages had retained its own 

 character, the one yielding large plaques, the other, minute ones. If 

 the bacteriophage were a product of the bacterium, unquestionably 

 the two should have become uniform. As this did not happen, Asheshov 

 concluded that the bacteriophage is an autonomous entity, independent 

 of the bacterium at the expense of which it multiplies. 



VII. Gratia and de Namur"^ have made use of bacteriophage races 

 particularly well adapted to demonstrating the fixity of characters as 

 well as the autonomy of the bacteriophage. For their experiment they 

 selected the polyvirulent Staphjdo-bacteriophage, race h, active for all 

 strains of albus, aureus, and citreus, and a second Staphylo-bacterio- 

 phage, race v, whose virulence is strictly limited to a single Staphylococ- 

 cus albus, strain V. They subjected the polyvirulent bacteriophage h 

 to a series of passages at the expense of staphylococcus V, and found 

 that its properties were retained intact. 



Inasmuch as this experiment seemed particularly well adapted to 

 demonstrate the point, I have repeated it, using eveiy precaution to 

 forestall objections.^^° 



Incidentally, it may be well to point out that for an experiment of this 

 type to be beyond criticism, it is necessary to carry the race of bacterio- 

 phage (here, race h) through a sufficient number of passages with the 

 given bacterium (here, strain V) so that by virtue of the successive dilu- 

 tions it will be impossible that any of the original liquid containing the 



