TWENTY-FIVE YEARS OF BACTERIOLOGY 139 



sence of their investigations consisted in injecting through 

 the trachea into the lungs of rabbits saline nasopharyngeal 

 washings derived within the first 24 to 36 hours after the 

 appearance of symptoms from influenza patients and ob- 

 serving the effects (a) upon the blood and (b) upon the 

 lungs. The striking changes, in the successful experi- 

 ments, relate to the white corpuscles of the circulating 

 blood which suffer a numerical depression affecting chiefly 

 the mononuclear type of cells, and to the lungs in which 

 multiple hemorrhages and edema, but not pneumonia, 

 arise. The effects are correlated: where no lung lesions 

 are found no blood alterations occur. These objective 

 phenomena are induced by filtered materials free of all 

 ordinary bacteria (aerobic and anaerobic) and they have 

 not been secured otherwise than with materials derived 

 from early cases of epidemic influenza ; but when present, 

 the rabbits affected very readily become subject to the 

 action of various other bacteria (streptococci, pneumo- 

 cocci, staphylococci, influenza bacilli), to which they are 

 otherwise resistant, but which then settle in the lungs and 

 excite fatal pneumonic affections. The unassisted action 

 of the influenzal material is not fatal ; only when an ordi- 

 nary bacterial lung infection is superadded does death 

 follow. All who are familiar with the effects in man of 

 pure influenza and then of influenza complicated with 

 pneumonia of pneumococcal, streptococcal, etc., origin 

 will appreciate this distinction. 



What also characterizes the class of diseases incited by 

 the true filterable parasites in their high degree of speci- 

 ficity and the enduring immunity which follows recovery 

 from an attack. This is true among animals, for instance, 

 of hog cholera and foot and mouth disease, and in man 

 of poliomyelitis. This specificity is shown by the difficulty 

 or impossibility of implanting the virus on specifically re- 

 mote animals. In poliomyelitis, for example, only mon- 

 keys are subject to experimental infection, in hog cholera 

 and foot and mouth disease, only swine and cattle. Bear- 



