190 



only 2 of these rats had died. The others were alive and appar- 

 ently well. 



One objection to these agents which I have not seen stated is the 

 following: The lesions caused by at least some of these members of 

 the para-colon group may readily be mistaken for the lesions of 

 plague, or it will perhaps be more accurate to say they give rise to 

 lesions that create in one's mind a suspicion of plague infection, 

 and I have had to put many a rat to the guinea-pig test in order to 

 make certain that a Danysz infection was not associated with the 

 infection of plague, or that a Danysz rat was not a plague rat. Of 

 course, this is of no consequence except in a community where anti- 

 plague measures are being taken, and an observer of limited experi- 

 ence who did not put a rat to a pretty rigid test would probably call 

 some plague infected when in reality such is not the case. 



In addition to the data set forth in this report, I have on several 

 occasions fed the tissue of rats dead of Danysz infection to other 

 rats, but have never succeeded in reproducing the disease. In other 

 words, I have had no success whatever in raising the virulence by 

 passage through animals. 



OPINIONS OF OTHERS. 



Kitasato, a 1906, states that the typhoid bacillus of the rat, which 

 has been effectively used for killing field mice, has been found useless 

 for house rats ( Mus rattus) and therefore they no longer employ it. 



Melvin, 6 1908, reports that recently several new rat viruses were 

 investigated in the Bureau of Animal Industry, with the result that 

 the experiments clearly demonstrated the ineffectiveness and unre- 

 liability of the preparations tested. 



Rabiger and Schwinning, c 1906, tested the culture discovered 

 by G. Neumann and prepared by the joint stock company "Ratin" 

 at Copenhagen by applying it to rat destruction. Of house rats 90 

 per cent died; black rats 42.9 per cent; while horses, dogs, goats, 

 sheep, fowls, and pigeons suffered no harm. Of seven experiments 

 practically carried out, six showed very good results; in one favor- 

 able results were absent, which agrees with the experiments made in 

 Denmark. There it was likewise found that in individual locally 

 limited places the rats were able absolutely to withstand the infec- 

 tion of ratin. 



a Kitasato, S.: Combating plague in Japan. Philippine Journ. Sci., vol. 1, 1906, 

 p. 465. 



b Melvin, A. D.: Report of the Chief of the Bureau of Animal Industry for 1908. 

 Washington, 1908. 



c Rabiger and Sch winning: Versuche mit Ratin, einem neuen Ratten totenden 

 Bacillus. Mitth. d. deutsch. Landw.-Gesellsch., 1906, No. 18. Rev. by Ehrenberg 

 in Centblt. f. Bakt., 2. Abt., vol. 18, 1907, p. 375. 



