124 



TiJE ameeica:n MOKTHLY 



[July, 



us. To test the extent to which the 

 virus may be diluted, we inoculate 

 healthy fowls with a drop of various 

 dilutions of our cultivation-liquid, ob- 

 tained as above, and which may be 

 called the first generation, and we 

 find that a dilution of i to 2000 al- 

 most invariably produces death. The 

 virulence of a first cultivation then 

 proves nothing, and we must stop to 

 inquire the extent to which such vi- 

 rulent liquids may be diluted and still 

 prove fatal when there is no opportu- 

 nity for reproduction. Experiments 

 show that death is frequently pro- 

 duced by dilutions of fowl cholera 

 virus of 10,000 but rarely by those of 

 I to 20,000 or I to 40,000, and sel- 

 dom, if ever, by greater dilutions. 



We are now in a position to judge 

 if the virus really multiplies as we 

 know the bacteria do. We have found 

 the extent to which the first genera- 

 tion must be diluted to destroy its vi- 

 rulence and we make a second culti- 

 vation which dilutes the first as the 

 first dilutes the blood ; after twenty- 

 four hours, we start a third cultiva- 

 tion, and now the first is diluted in 

 the proportion of i to 4,000,000, or 

 far beyond the extent to which it was 

 found possible to dilute it without de- 

 stroying its properties when no culti- 

 vation was allowed. Have we in this 

 case destroyed the virulence ? No, 

 indeed; a single drop of the third, 

 fourth, fifth or sixth cultivation will 

 destroy ten thousand fowls as surely 

 as a drop of the first. The virus has 

 been cultivated then, has multiplied, 

 and is capable of indefinite multipli- 

 cation. Our liquid swarms with mi- 

 crococci and nothing else can be 

 found by the most careful micro- 

 scopic examination. If we expose 

 virulent liquids to atmospheric germs, 

 putrefaction soon occurs and their ac- 

 tivity is lost. Why has not the same 

 result followed in our cultivation li- 

 quids if the bacteria multiplying in 

 them were foreign to the virus ? Have 

 we not, even here, a strong indication 

 that these organisms are the active 

 principle of the virus — that they pro- 

 duce the disease ? 



3. The living bacteria are required 

 to produce the malady. — There are 

 three hypotheses which one must take 

 into account in determining the active 

 principle of even this cultivated virus. 

 I. The pathogenic agent may be a solu- 

 ble ferment. 2. It may be living parti- 

 cles (bioplasm) extremely minute, or 

 having the same refractive index as 

 the liquid in which it multiplies, and 

 therefore invisible. 3. It may be the 

 bacteria to which our attention has 

 already been directed. Pasteur has 

 shown that by filtering the cultivated 

 virus through plaster, the solid parti- 

 cles are removed and the limped li- 

 quid which is obtained is perfectly 

 harmless, even when injected under 

 the skin of susceptible birds in con- 

 siderable quantities. Objection being 

 made to the filtering as liable to re- 

 move some dissolved bodies as well 

 as the solid particles, the same able 

 investigator has given us another and 

 very valuable demonstration. If tubes 

 containing cultivated virus are placed 

 where the temperature is constant, 

 the micrococci are all deposited on 

 the bottom of the apparatus, leaving a 

 perfectly limped liquid above them. 

 Inoculations with this liquid prove it 

 to be as harmless as that which has 

 been filtered.* 



Even this demonstration was insuf- 

 ficient to convince those who oppose 

 the germ-theory — the ferment might 

 be very volatile and escape from the 

 upper layers of the cultivation-liquid, 

 or it is attached to the bacteria them- 

 selves and can only be introduced with 

 them. To meet such objections the 

 writer has carried through an entirely 

 different line of investigation. It was 

 found after considerable experiment- 

 ing, that the activity of the virus is 

 destroyed at a temperature of 132" F. 

 if maintained for fifteen minutes — a 

 temperature so low that few, if any, 

 chemical bodies would be affected by 

 it if protected from atmospheric gases 

 and evaporation. Small glass tubes 

 were, therefore, completely filled 



* Bulletin dc FAcad/mie de Mt'decine, 1880, 

 P- 530. 



