1903-4. | ULTRAMICROSCOPIC ORGANISMS. 55 
The objection might have been raised to their interpretation of these 
results, that they were dealing with an excessively virulent soluble poison. 
To meet this objection they proceeded as follows. They found that the 
minimum infecting dose of the fluid from the vesicle was sod00 ¢c.c. They 
therefore, after diluting the lymph and passing it through the filter, in- 
oculated animal 1 with 35 c.c.; from the vesicles which developed upon 
this animal they collected the lymph, (about 3 c.c.) refiltered and inoculated 
a second animal with the same amount and so on through a series of six 
animals. Given the same amount of lymph collected in each case and the 
same dilution, we see that if it were only a poison the last animal would 
have received less than one two billionth of a c.c. of the original lymph. 
As it had been demonstrated that at least 5o$00 was necessary for infection 
it is evident that reproduction must have taken place. 
Another of these interesting organisms has been discovered by Nocard 
and Roux in the so-called contagious pleuro-pneumonia of cattle. The 
cause of this disease has been looked for by a number of investigators, but 
although numerous bacteria had been isolated, no one of them turned out 
upon further study to be the essential parasite. Nocard and Roux pro- 
ceeded to investigate in a somewhat different manner. They demonstrated 
that the contagium was present in the serous effusion in the pleural cavity 
and in the lungs, but again could see nothing; they therefore tried this 
experiment. A sterilized collodion capsule, a little larger than a ten grain 
quinine capsule, was filled with sterilized bouillon, inoculated with a trace 
of the serous fluid and placed by operation in the peritoneal cavity of a 
rabbit. After a time it was removed and was found to have become milky 
or opalescent. In this opalescent fluid, it was shown by inoculation the 
organism was present in increased numbers and upon microscopic exami- 
nation it was possible to see enormous numbers of minute dancing points, 
so small that no structure could be made out with the highest magnification. 
This virus would also pass through a Pasteur filter. Here we have a para- 
site just upon the borders of visibility. 
Somewhat later, Beyerinck, a Dutch bacteriologist turned his atten- 
tion to a curious disease of the tobacco plant, the so-called mosaic disease. 
This disease produces as its prominent symptoms the destruction of the 
chlorophyll of the leaves with the result that they become covered with 
yellow spots. It can be transmitted from leaf to leaf and from plant to 
plant by inoculation, the slightest trace of juice from the mosaic spot 
being capable of setting up the trouble in another plant. 
Microscopic examination and culture methods were unsuccessful in 
revealing any bacterial organisms. The juice seemed absolutely clear and 
transparent, under the highest magnifications, although evidently very 
contagious. Beyerinck applied the filter test, and found the filtered 
