108 SIXTEENTH REPORT. 



to its having a longer duration of infection than that in the rats. Sometimes 

 the animals died without showing any reappearance of the organism in 

 their blood. 



As the animals were examined only twice a week, no definite information 

 can be given as to when these organisms disappeared from the blood and 

 when it reappeared in it. If the animal was positive once it will in most 

 cases be positive again. 



The value of any record depends upon the authenticity of its various items. 

 In this case, the series of inoculations and examinations, extending over a 

 period of seven years, were made by seven or eight individuals, not as an 

 experiment, but as a part of a laboratory routine. The fact that with a 

 few exceptions of a minor importance as far as the above compilation is 

 concerned, the record is complete, vouches for the accuracy and complete- 

 ness of note taking. All the records were made at the Hygienic laboratory 

 under the immediate supervision of Prof. F. G. Novy and the credit belongs 

 to him for the trustworthiness of the records. This summary was made at 

 his suggestion. It is hoped that its publication will stimulate similar compila- 

 tion from other laboratories to the end that comparisons of the virulence 

 of the various strains of this species and of other species, even after a long 

 laboratory culture will be made possible. 



A preUminary report was given at the spring meeting of 1913 of Michi- 

 gan Academy of Science, but publication was deferred to allow complete 

 summary of the data to be made. 



East Lansing, Michigan, 1914. 



