Isolation 



The cover-glasses are immersed in the solution, and kept 

 in the incubator for from three to six hours, after which they 

 are washed in water, dried, and mounted in Canada balsam. 

 By this method the erythrocytes are stained red, the leuko- 

 cytes blue; and the bacilli, also blue, appear as short rods 

 or as dumb-bells. 



Large numbers of bacilli may be present, though some- 

 times only a few can be found after prolonged search, as they 

 are prone to occur in widely scattered but dense clusters. 

 They are frequently inclosed within the leukocytes. It is 



Fig. 166. Bacillus of influenza. Smear from sputum. (After Heim.) 



scarcely necessary to pursue so tedious a staining method for 

 demonstrating the bacilli, for they stain well enough for recog- 

 nition by ordinary methods. 



Isolation. The influenza bacillus grows poorly upon 

 artificial culture-media, and is not easy to isolate, because 

 the associated bacteria tend to outgrow it. When isolated 

 it is difficult to keep, as it soon dies in unnatural environ- 

 ment. 



Pfeiffer found that the organism grew when he spread pus 

 from the bronchial secretions upon serum-agar. Subcul- 

 tures made from the original colonies did not "take." It 

 therefore seemed as though it might depend upon the absence 

 of some ingredient that the bronchial secretions contained. 



