106 Report of the Department of Bacteriology of the 



in two or more samples and in such numbers as to make it evi- 

 dent that they were fairly permanent inhabitants of the udder. 

 There is little reason to doubt but that the forms thus isolated 

 are true members of the udder flora. 



Feeling that more extensive observations should be made, 184 

 samples were obtained on a single occasion from 46 cows in 

 another herd. In this case the samples were drawn into sterile 

 test tubes by either one of us (W) or by Dr. R. S. Breed. Hav- 

 ing but a single sample from each quarter of the udder there was 

 no opportunity for observing the persistence of a given form. 

 All plates showing evidence of contamination were rejected and 

 only those types of colonies which were present in considerable 

 numbers were selected for study. While the attempt was made to 

 exclude all contaminating forms there remains the possibility 

 that some of the forms thus selected were not true members of 

 the udder flora. 



In any work of this nature the personal element is necessarily 

 large. Success in separating the colonies upon any plate into 

 classes, each of which represents a single group of organisms, re- 

 quires both experience and judgment. The ability to carry in 

 mind the distinguishing characteristics of a growing list of such 

 classes, so that the colonies present may be correctly assigned to 

 classes which were established months earlier, is especially diffi- 

 cult to acquire. The accuracy of this separation can be tested in 

 a measure by the extended study of representatives of these 

 classes and in this investigation cultures were thus studied in all 

 cases where doubt arose as to the proper classification. However, 

 on account of the large number of colonies which must be classified 

 and the amount of time consumed bv the detailed studv of se- 

 lected forms it follows that the classification records must depend 

 largely for their accuracy upon the judgment of the worker. 



One of the authors (W) devoted practically his entire atten- 

 tion for approximately one and one-half years to the examination 

 of samples from cows' udders and the classification of the forms 

 found there ; and he is to be held personally responsible for the 



