52 The Farmer'' 8 Veterinary Ad/oiser. 



germ is inherent in every tissue of the body, and not inere]y 

 in those parts that must be readied through an indurated 

 gland. Finally, this condensation of the gland, caused by 

 the infection of one disease, gives no protection against that 

 of a second. If the protection were due to a mere mechani- 

 cal obstruction, then the immunity acquired by an attack of 

 one disease would extend to all others having germs of 

 equal size ; whereas, with rare exceptions (cow-pox and small- 

 pox), no one contagious disease is vicarious of another. 



(D) The YrrAL Eesistance Theoet. This hypothesis 

 assumes that the living cells and nuclei of the blood and tis- 

 sues of the body, having once been subjected to the attack 

 of a specific disease-germ, acquire a power of tolerance or 

 resistance of that particular germ or its products which pre- 

 vents them from readily succumbing a second time to its 

 evil influence. 



The habit of tolerating an injurious agency without harm 

 is a matter of common experience. Exposure to the sun 

 after long seclusion in-doors blisters the face and liands, but 

 after continued exposure and tanning, it has no such effect. 

 Eowing, hoeing, or chopping will at first blister the hands, 

 but after some experience it only hardens and strengthens 

 them. The boy's first cigar or pipe of tobacco sickens him, 

 while the practised smoker can consume the poison from 

 morning to night. So with the drinker, the opium-eater, 

 the victim of the chloral-habit, and the arsenic-eater. Each . 

 of these comes to take with impunity that which would have 

 proved fatal in his early experience. 



So it is with the morbid products of the life of a disease- 

 germ. Coming for the first time in contact with the living 

 cells and nuclei of the body, they prove more or less potent 

 poisons, whereas later these can bear their presence with 

 comparative impunity. But in both cases alike the power 

 of resistance is limited. It is quite possible by an overdose 

 to kill the smoker, the drinker, the opium-eater, the chloral- 



