NATURE OF BACTERIOPHAGE 355 



the name Protobios bacteriophagus (syn. Bacteriophagum intestinale 

 d'Herelle) d'Herelle, IQIS.^^^-^^^ This infravisible microbe is the agent 

 of an infectious disease occurring among bacteria, and this disease is 

 bacteriophagy.* 



* It should be remembered, however, that although up to the present time 

 parasitism of bacteria has not been recognized we have for a long time observed 

 and studied many parasites which incite infectious disease among the protozoa. 

 Several examples will be found cited among the works of Metchnikoff . (Legons 

 sur la pathologie comparee de 1' inflammation, Paris, 1892, Masson & Cie. 

 L'immunite dans les maladies infectieuses, Paris, 1901, Masson & Cie.) 



It may be well to mention a study of Dangeard entitled "Sur les parasites du 

 noyau et du protoplasma" (Le Botaniste, 1894/95, 4, 199-248) for the facts 

 disclosed by this investigator offer certain analogies to those presented in the 

 preceding chapters. But there are these differences, namely, the parasite of 

 Dangeard attacks a protozoan, and its dimensions are such that it can be readily 

 observed microscopically and therefore classified. 



The observations of Dangeard deal with an Oomycete, Nucleophaga amoeba 

 Dangeard, which parasitizes the nucleus of Amoeba verrucosa Ehr. The Amoeba 

 verrucosa has a large, doubly-contoured spherical nucleus, and also a nucleolus, 

 likewise spherical, whose diameter is about two-thirds that of the nucleus. The 

 substance of the nucleolus is very dense and stains with great intensity with 

 various nuclear staining reagents. Between the nucleolus and the nuclear mem- 

 brane is a space filled with the nuclear fluid. 



The zoospore of Nucleophaga amoeba first penetrates the protoplasm of the 

 amoeba but it never develops there; it passes into the nucleus through the mem- 

 brane which it perforates, most certainly through the aid of a dissolving diastase. 

 Dangeard has demonstrated the portal of entrance of the parasite as a minute 

 circular opening, as though made by a punch, persisting after the entrance of the 

 parasite. After its penetration into the nucleolus the parasite resembles a re- 

 fractile corpuscle, increasing slowly in size in proportion as the nuclear substance 

 disappears. When this nuclear material has been utilized completely the entire 

 interior of the nucleus is filled and the membrane is distended. At this time the 

 nucleus of the parasite, up to the present time single, actively divides and when 

 sporulation is effected there are about one hundred regularly spaced nuclei. 

 About each of these nuclei a zoospore organizes, and a sporangium is thus formed, 

 containing distinct, rounded corpuscles, which contain nuclei at the time of 

 sporulation. 



Frequently a single amoeba is parasitized by two or perhaps several zoospores, 

 and in such cases each develops separately and gives birth to a distinct sporan- 

 gium. When the sporangium reaches maturity the protoplasm of the amoeba 

 disintegrates, the sporangium ruptures, freeing the young zoospores, and these 

 become distributed throughout the medium, ready to parasitize the healthy 

 amoebae in their neighborhood. 



It is evident that I have not made any comparison between Nucleophaga amoeba 

 and Protobios bacteriophagus, and that these observations are mentioned simply 

 because there is a certain resemblance between the two phenomena of destruc- 

 tion, — that of the amoeba and that of the bacterium. 



