67 
REMARKS OR EILTRATION EXPERIMENTS WITH YELLOW-EEVER BLOOD. 
We have been careful to give with some minuteness all the details 
of the manner in which the blood was filtered in these experiments. 
We know that the filtration of micro-organisms or other small parti¬ 
cles through porcelain or diatomaceous earth is influenced very much 
by the length of time the filtration is continued, the pressure used, by 
the character of the fluid in which the particles are suspended, the 
temperature, and other factors which are perhaps less known. 
Our review of the literature on the filtration of blood and body 
juices containing the infectious material of diseases, the causes of 
which are unknown and which are believed to be ultramicroscopic, 
disclosed reports of successful and unsuccessful filtration with such 
meager details that it is difficult to draw proper conclusions. Those 
factors which control the poiver of a given filter to allow an organism 
to pass or to hold it back also account for the different results which 
various experimenters have obtained in certain cases. 
For instance, we succeeded in passing diluted yellow-fever serum 
through the closest-grained Pasteur-Chamberland B filter that we 
could obtain, whereas the French commission—Marchoux, Salimbeni, 
and Simond—working at Rio de Janeiro, failed to pass the infective 
agent of yellow fever through a Chamberland B filter, though they 
found that it did pass through the Chamberland F filter,. As the 
French commission used undiluted blood and we used diluted serum, 
the apparent discrepancy in results is accounted for; for it is a well- 
known fact that particles suspended in an albuminous medium filter 
with more difficulty than particles suspended in water, alcohol, or 
other limpid menstra of this character. 
Nocard, Roux, and Dujardin-Beaumetz, in 1899, endeavored to 
repeat Loffler’s experiment with aphthous fever. They first failed to 
pass the infective agent contained in the lymph of this disease through 
a Berkefeld filter because they used an albuminous fluid, viz, “ Mar¬ 
tin’s serum-bouillon,” in order to dilute the lymph with a nutrient 
medium, thus hoping to obtain cultures without the danger of con¬ 
tamination in the filtrate. They found, however, that the albuminous 
matter contained in the diluting fluid clogged the pores of the filter, 
so that the filtrate was not virulent. 
They repeated the experiment, using water to dilute the lymph in 
the proportion of 1 to 50, when they found the organisms causing 
aphthous fever readily passed through a Berkefeld filter, and gave the 
disease by intravenous injection to young and old cattle. 
It is also a well-known fact that filters which successfully hold 
back certain bacteria will permit them to pass if the filtration is con- 
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