BEHAVIOR OF BACTERIOPHAGE IN DISEASE 489 



The conditions being less favorable for the bacteriophage, its viru- 

 lence increases less rapidly, bacteriophagy takes place after a longer 

 latent period; the result being that after a few mUd symptoms, the 

 disease is aborted. 



When the virulence of the bacteriophage is built up only after a con- 

 siderable delay, the disease follows its course up to that time when the 

 acquired virulence permits a complete bacteriophagy; the result being 

 that at this time the symptoms of the disease regress, disappear, and the 

 individual enters upon convalescence. 



When the virulence of the bacteriophage is enhanced very slowly and 

 the delay in increased activity permits the bacterium to acquire a 

 resistance, or when the bacterium at the time of invasion already has a 

 resistance acquired outside of the body now invaded, a struggle takes 

 place, the contending forces being the virulence of the bacteriophage 

 on one hand and the resistance of the bacterium on the other, and the 

 condition of the patient reflects the ups and downs of this campaign. 

 The result here may vary ; if the conditions of environment and heredity 

 favor the bacteriophage, the virulence permanently overcomes the 

 resistance, complete bacteriophagy takes place; convalescence is es- 

 tablished. If, on the contrary, the conditions favor the bacterium, it 

 acquires a refractory state, it is able to develop without hindrance; the 

 individual dies. 



When, as a last possibility, the intestinal bacteriophage remains inert, 

 the bacterium develops freely without any necessity for acquir- 

 ing a resistance; the result being the death of the individual 

 (d'Herelle='ii'3i3'3i^'3^''32.)_ 



The bacteriophage does not remain confined to the intestine; it passes 

 into the circulation, from there into the tissues, and thence to the lesions 

 where bacteria are to be found upon which it can exert its faculty of 

 assimilation ; the result being an in vivo bacteriophagy with an elimina- 

 tion of the invading microbe. This is what takes place in experimental 

 typhoid infection of the rat (d'Herelle^^^) ; in avian typhosis (d'Her- 

 elle'^21). in bubonic plague (d'Herelle^^i) . i^ typhoid fever (Beckerich 

 and Hauduroy^^); in staphylococcus infections (d'Herelle^^O ; and in 

 streptococcus infections (Eichhoff). 



The process of in vivo bacteriophagy is not restricted to animals. It 

 also occurs in plants, as in the case of the Leguminosae infected with 

 B. radicicola (Gerretsen, Sack, Gryns, and Sohngen^-^). 



