blood-corpuscles in yellow fever, which he has named Paraplasma flavigenum, and which he regards as the germ of the disease. So far, this claim has not been accepted by yellow-fever experts, and is not supported by convincing experimental evidence.
Nature of the yellow - fever germ indicated by epidemiology.— In earlier editions of this book I remarked, " The reasons for the peculiar geographical limitation of yellow fever are but partially understood. A principal reason, undoubtedly, is that yellow fever belongs to a somewhat restricted class of diseases which, though communicable, are not directly so through immediate conduction from sick to sound; diseases whose germs do not pass quickly from the sick to the healthy, like those of scarlatina and smallpox, but have first, apparently, to undergo extracorporeally developmental changes that enable them to attack and to live in the human body. Such diseases, seeing that their propagation demands an additional condition— the extracorporeal state or medium— must necessarily be more difficult to acquire, must spread more slowly, and be more limited geographically, than the ordinary infectious diseases." These remarks, suggested by the peculiar epidemiological features of yellow fever, have received remarkable confirmation from the brilliant work of Reed, Carroll, Agramonte, and Guiteras, and by many subsequent workers.
The germ occurs in the blood.— This has been incontestably demonstrated by Reed, Carroll, and Agramonte. They injected into six non-immunes blood from yellow-fever patients. In this way, in five instances, they conferred the disease within the recognized limits of the incubation period. In another experiment they induced yellow fever by injection of defibrinated blood. By other experiments they showed that the virulence of the blood was destroyed by a temperature of 55° C. Another point, already alluded to, is that these experiments, taken in conjunction with others to be presently described, showed that the germ is present in the blood, at all events in a transferable state, only during the first
