173 
carditis lenta in a child, where I did not find streptococci in the 
blood. 
The epidemic had nearly reached its end, and | should not have 
been able to continue my researches if not a happy coincidence, a 
wrong hypothesis, as appeared afterwards, had helped me on. 
Starting from the fact, observed by myself and also by other 
investigators, that inoculation of dead bacteria, which complicate the 
influenza, so pneumo- and streptococci or influenza-bacilli, on persons 
not only protects them against complications, but also against the 
influenza itself, I thought that the virus of the influenza would 
probably be present in the cultures in broth with blood of strepto- 
and pneumococci, collected by Dr. Snapper and myself, and so | 
tried to separate the virus by filtration through a Berkefeld-filter 
and inoculation into broth with blood. It actually succeeded the first 
times. I obtained liquids in which no ordinary bacteria were 
present, but which became turbid at 37° C. My results were however 
varying, at one time the liquid became turbid, at another time it 
did not. 
After first having ascribed these varying results to the Berkefeld 
filters, it became evident afterwards that the presence or the 
absence of the turbidness was dependent on an addition of a small 
quantity of hemoglobin and now the riddle was soon solved. If one 
adds to the broth a liquid containing a small quantity of hemoglobin, 
this mixture remains clear at room-temperature, but it becomes 
turbid in the incubator after 24 hours. This turbidness is also for- 
med in peptone, even in salt solution; the latter must be however 
very precisely neutral, because otherwise the turbidness is not ob- 
served. The hemoglobin solution was always made by washing ery- 
throcytes with salt solution, then dissolvlng them in distilled water 
and filtering through a Berkefeld-filter. It is easy to give an expla- 
nation, why this turbidness is obtained in blood from serious 
influenza patients; in this illness a slight hemolysis of the blood 
arises intra vitam through the secondary hemolytic streptococci, and 
the blood we add to the broth will contain not only red blood 
corpuscles, but also hemoglobin, free in the ‘plasma. And this is 
broken up in the incubator. 
To prove this more closely I prepared the carotis of a rabbit free, 
let a few drops of blood flow into the broth and into a test tube (1). 
Then I injected distilled water in the earvein and shortly after- 
wards blood was drawn from the carotis and mixed in the broth 
and in a test tube (II). The tubes with broth were put in an incu- 
bator. I let the blood, which was received in the testtubes, coagulate; 
. 12* 
