DISEASES OF SWINE AND OTHER ANIMALS. 1^9 



slight, without any apparent cause for such dilierence. Sometimes an 

 epidemic begins with moderation and closes with severity, and vice versa. -^ 



Trousseau holds : "That every contageous disease must have a spon- 

 taneous development, as contagion necessarily implies the presence of 

 two individuals, one the giver, the other the receiver, of the morbiiio 

 germ." This remark he follows by another which modifies it : " While 

 there is every reason to beheve," he says, '^ that at present there are 

 some diseases, such as syphilis, small-pox, and measles, that are always 

 reproduced by contagion, there are other maladies which we see arise 

 spontaneously." 



I believe it is now generally conceded that all diseases that pass 

 through a regular period of incubation are contagious or infectious, and 

 that they depend upon a morbific germ for their development. In sev- 

 eral of the contagious diseases the morbific germ has been discovered 

 by the microscope, and in all i)robabihty the morbific germ in all conta- 

 gious diseases wiU yet be discovered, as has already been the case in 

 the measles, small-pox, whooping-cough, scarlatina, typhus and typhoid 

 fevers. 



Lubermeister, iu his uitroductory remarks on acute infectious diseases, 

 says " that a peculiarity of infectious diseases, which they have in com- 

 mon with the poisons proper, or intoxications, but by which they also 

 differ iu the most marked manner from all other diseases in their spe- 

 cificness, which shows itself in the fact that always and under all cir- 

 cumstances a given kind of disease is solely due to a given kind of 

 morbid agent or cause. There is no such constancy between cause and 

 manifestations in other diseases. Exposure to different degrees of cold 

 will produce diHerent affections. * * * (jn the oth^er hand, vaccina- 

 tion with the vu'us of variola only produces variola, if a-ny disease at 

 all is produced by it ; vaccination with the vaccine matter only produces 

 vaccinia ; the infection from a ijaticut with measles only produces mea- 

 sles, and never anything else, and vice versa. Whoever, therefore, is 

 affected with small-pox, measles, syphilis, »&c., is certaiu that he has 

 taken the disease by becoming infected with small-pox, measles, syph- 

 ilis, &c., and of no other disease. In infectious diseases the predis- 

 posing cause, which in most other diseases plays a more important part 

 than the exciting cause, is to be considered onbf in so far as it may de- 

 termine the severity of the disease. The kind of disease is entu'ely in- 

 dependent of it. Various physiological conditions may induce other 

 pre-existing affections, and are intiuential in so far as they may increase 

 or diminish the susceptibility, but the kind of disease will not be de- 

 termiued by it. 



"Through the longest series of generations diseases preserve their spe- 

 cific character ^\ ith the utmost persistenc;\', and if at times some of these 

 characteristics ai-e not brought into complete matimty, owing to an un- 

 favorable field for their development, they assume them again as soon 

 as they are planted in favorable soil. The weather, the period of the 

 year, the climate, the conditions of the soil, <S:c., conduce to, or prevent 

 the spread of, an infectious disease, 1)ut they never change the nature 

 of the disease. The kind of diet and all other idiysio-chemical infiueuces 

 act indifferently with regard to the nature of the allc'Ctioii, and one in- 

 fectious disease is never changed into another. The doctrine of si)ecilic- 

 ness woidd arise, as a necessary conse<][uence, from the hypothesis of a 

 contagion vivum, even if it were not already proved by the facts. From 

 the specificness of infectious diseases we naturally conclude that they 

 never arise spontaneously, but are dependent upon a transmission ox 

 continued i^ropagation of the diseased person." 



