50 THE LUNG PLAGUE OF CATTLE. 



and Duguid found that injections of virulent lymph into the blood 

 usually rested without any local effect whatever, and we have appar- 

 ently solid ground for the hypothesis that the germ of this disease does 

 not well survive in the blood. Tentatively, we may call it a bacteridiau 

 infection of the connective tissue and lymphatic system, which may be 

 localized in any part of the body supplied with these structures, but is 

 usually seated in the lungs, from the germ being taken in with the in- 

 spired air. 



CONVALESCENT CATTLE DANGEROUS FROM ENCYSTED MASSES OF 



DISEASED LUNG. 



Animals that have apparently recovered from lung plague are usu- 

 ally supposed to be perfectly safe, and even specially valuable in in- 

 fected districts, because they -will not take the disease a second time. 

 Yet there is reason to suppose that many such become bearers of the 

 infection to healthy stock with which they mingle, and being exempt 

 from suspicion admission to sound herds is freely conceded them. 



The explanation of 'this is probably to be found in the condition of the 

 lung usually left after an apparent recovery. The tendency of the dis- 

 ease is to the plugging of the blood-vessels in those parts of the lung 

 which are most violently inflamed, to the death of such portions for lack 

 of their nutrient supply, and, finally, in case of recovery, to the encyst- 

 ing of the dead mass in a thick, fibrous sac, which completely cuts it 

 off from the adjacent parts of the organ. The seclusion of this seques- 

 trum is complete; no air, save such as can permeate the membrane, and 

 no aerial germs being allowed access to its substance. It therefore un- 

 dergoes no ordinary putrefaction, and after long encystment its faint, pe- 

 culiar, and slightly mawkish odor is in marked contrast with the intol- 

 erable fetor of the ordinary gangrenous lung, in which the aerial bacte- 

 ria of putrefaction have been working! These dead masses of the hepa- 

 tized lung, in cases of apparent recovery from lung plague may remain 

 encysted for from six to fifteen months, undergoing very little change, 

 apart from a very slow liquefaction on the surface of the mass, and a 

 corresponding contraction of the investing sac. At the commencement 

 of recovery more than half of a lung may be thus encysted, and six and 

 even ten months later masses of one or two pounds are frequently 

 found awaiting the slow process of liquefaction. 



In cases of perfect recovery this process of liquefaction is completed, 

 and the liquid being absorbed, there is left but a soft, cheesy-looking 

 mass of whitish, or yellowish-white debris. The important question is, 

 how long the encysted mass remains infecting after it has been encap- 

 suled and shut off from all other parts of the lung, and after the bearer 

 has apparently recovered f 



On this point it must be borne in mind that the encysted portion of 

 the diseased lung was filled with the virulent gerrns at the period of en- 

 eystment, and having been from that time shut off from all the processes 

 of nutrition, or physiological change, and having been equally protected 

 against the access of bacterial or other germs from without that might 

 have preyed upon and destroyed the virulent ones, there is a strong 

 presumption that these virulent lung-plague germs, or their descend- 

 ants, remain unchanged from their infecting condition, as when first 

 encysted. 



We may find a tolerably fair counterpart of this condition in the 

 masses of tubercle frequently found in the internal organs of consumptive 

 men and animals. The deposited tuberculous mass is not traversed by 



