42 DISEASES OF SWINE AND OTHER ANIMALS. 



As to the distaiico -wliioli tlie infections i^rinciplc can be conveyed 

 tlirougli llie air, I cannot make any accnrate statements, bnt liave rea- 

 sons to believe tliat swine located a distance of one mile from any dis- 

 eased lierd Vvillbe safe. To decide tliis])oint, wliicli is of very great im- 

 portance, requires careful experiments. 



The nature of the infectious or contagious principle. — The experiments 

 mtli pigs A and 0, though not conclusive and needing re])etition, indi- 

 cate very strongly, as has already been mentioned, that the hacllll and 

 their germs found invariably in tlie blood, in the morbidly changed tis- 

 sues, and in the excretions of the diseased swine, must constitute the 

 infectious or contagious principle of swine-plague. I, for my ])art, am 

 convinced that such is the case. Still I should hesitate to express this 

 opinion if it was supported only by those experiments and not by other 

 facts, such as the peculiarities in the spreading of the disease, the man- 

 ner in which the infectious principle is acting and is communicated to 

 healthy animals, and the workings of the morbid process. (See next 

 chapter.) At any rate, if the hacilU and bacillus-germs constitute the 

 infectious principle, all the strange features of swine-i^lagiie find a satis- 

 factory explanation; but if the infectious principle consists in an un- 

 known and mysterious chemical something, the peculiarities of the dis- 

 ease arc, to say the least, enveloped in mystery and cannot be explained. 

 What Professor Beale calls bioplasm could not be discovered under the 

 microscope. 



In want of a better name I have called the hacllll " hacllll .s?/?'.?," be- 

 cause the same, as far as I have been able to learn, are peculiar to and 

 characteristic of swine-plague. The baciUus-germs are small round 

 bodies of — as near as I can figiu-e without the aid of a micrometer — 

 about 0.0007 millimeter diameter, and reflect the light very strongly. 

 The hacllll suis are small, almost straight, cvlindrical bodies of about 

 0.003 to 0.005 millimeter in length, and 0.0007 to 0.0008 millimeter in 

 thickness, sometimes moving and sometimes without motion, and in cer- 

 tain stages of development slightly moniiiform, but in others apparently 

 not. (See drawings.) 



The causes. — Whether the disease is caused exclusively by infection — 

 by the hacllU and their germs being conveyed directly or indirectly from 

 diseased animals to healthy ones — or whether those hacllU suls and their 

 germs can be produced independently from, and outside of, the organ- 

 ism of swine; whether, in other words, swine-plague is a piu'e contagion, 

 caused exclusively by means of the infectious or contagious principle, 

 or can develop spontaneously, is a very important question, which can 

 be solved only by protracted experiments, and may not be solved at all 

 until the question as to whether a '-^ (jencratlo cquiroca'^ is possible or 

 actually taking place or not has found a, definite solution. If the hacilli 

 suis and their germs constitute the sole cause of swine-plague, as they 

 undoubtedly do, the disease must be considered as a x)ure contagion, 

 like many other contagious or infectious diseases, not capable of a pro- 

 topathic or spontaneous development, as long as the possibility of a 

 '■'■ gcneratlo equivoca^^ is denied, but if the latter is admitted, or proved 

 to be taking place, a spontaneous development must be considered not 

 only as possible but also as very probable. 



If the conclusions I have arrived at concerning the cause of the dis- 

 ease are correct, and I have scarcely any doubt they are, the question 

 as to the causes has been solved. Still, as a positive knowledge of the 

 true cause or causes is of the greatest importance, and as my experi- 

 ments are not numerous enough to be absolutely conclusive, further 

 investigations and more experiments of the same, or of similar kind, will 



