Contagious and Epizootic Diseases. 65 



ance, and to digest and dissolve them in preparation for 

 their consumption by the ravenous bacteridia. In their 

 tnrn tlie well-nourished bacteridia produce the ferment and 

 poison in increasing amount, and thus the strength of the 

 invading germs is increased relatively to the waning power 

 of vital resistance in the body until the whole economy is 

 fatally invaded and the victim perishes. 



The overwhelming action of these chemical products is 

 seen in the sudden death which ensues when a large dose of 

 virulent fluid is thrown into the body, no time being 

 allowed for the development and increase of the living 

 germs. On the contrary, when a small dose only is intro- 

 duced, illness is delayed much longer until the germs have 

 had time to multiply and produce their chemical products, 

 and death, if it occurs at all, is at a much later date. Some 

 germs, when thrown at once into the veins, produce no dis- 

 ease at all, but are destroyed by the ferments of the vital 

 fluid and the myriads of living blood-globules with which 

 they are brought rapidly into contact, and over the whole 

 body of which their chemical products can exercise no ap- 

 preciable effect. Yet the virus of lung-plague or of black- 

 quarter, deadly when introduced into the tissues but harm- 

 less when thrown into the blood, have, nevertheless, in the 

 latter case, the effect of conferring upon the entire system 

 the power of subsequent resistance to the same poison, so 

 that if later introduced into the tissues it rests innocuous. 

 Again, in the animal that has passed through a non-recurring 

 contagious disease without dying, a similar exposui-e to the 

 same poison later is harmless. This cannot be due to a 

 greater vigor of constitution, for the system, permanently 

 weakened by a first attack of a plague, still fails to contract 

 the same disease on exposure to even a more potent virus. 

 It can only be that the system has learned by its previous 

 experience to resist the organic poison which proved so 

 hurtful to it before. 



