TKANSACTIONS OF SECTIOX I. 813 



The evidence is brielly as follows: micro-organisms produce chemical sub- 

 stances or toxiues which have certain physiological effects ; these toxines cannot 

 increase without the presence of micro-organisms ; if, then, the micro-organisms 



in which there appears to be evidence of the presence of organisms too small to be 

 seen by the microscope are foot-and-mouth disease, the contagious pleuro-pneumonia 

 of cattle, and South African horse-sickness. 



(1) Foot-and-mouth Disease. — LoefBer and Frosch ' have shown that the lymph 

 from the vesicles in the mouth of an infected animal if filtered through a Berkefcld 

 filter still in a dose of ^l c.c. killed a calf in the same time as the unfiltered lymph. 

 This experiment was controlled as to the impermeability of the filter by infecting 

 the lymph before filtration by a culture of a very minute bacterium which did not 

 pass through the filter. The highest microscopic power failed to detect anything in 

 the filtrate. They found, however, that if the lymph were mixed with a fluid more 

 rich in albumen than the lymph itself, then the filtrate lost its infectiveness. 



(2) Plcuro-2»icumoma. — Nocard ^ found that the pleural effusion mixed with water 

 if filtered through a Berkefeld or a Chamberland ' F ' was still infective, but in such 

 watery fluids it was arrested by the Chamberland ' B ' and by the Kitasato. He 

 further found that there were in the infective filtrate refractile particles, which, 

 however, could not be resolved by a magnification of 2,000 diameters, but which he 

 considered might be the infective agents. 



(3) Horsc-!tlokness.— l!li.c¥a,Ajea.n^ found that the diluted blood of an infected 

 horse could pass through a Berkefeld and through a Chamberland ' F ' and still re- 

 main infective ; and, further, that if the blood of a horse which had died from this 

 infection were filtered through a Chamberland ' B ' it was still infective and killed a 

 horse in the same time as the original filtrate. Again microscopically nothing could 

 be seen, and again the efficacy of the filters was controlled by mixing the blood to 

 be tested with putrefactive organisms which the filter kept back as usual. Nocard ' 

 in one case says that blood can be freed of this infection by filtration, but 

 SIcFadyean's experiments are very numerous and so carefully done that this one 

 negative instance may be explained by want of susceptibility in the animal used. 



Of course the great difficulty is to be sure that the filters were efficient and had 

 no cracks, which such filters are very apt to have, but the work has been so carefully 

 controlled that this source of error may be excluded. The remaining source of ob- 

 jection is that the pathogenic agent might not be a bacterium but its toxine. The 

 most important experiments here are those of McFadyean, who filtered the blood of 

 horses infected with filtered blood and found it still infective ; and also those of 

 Loeffler, who goes carefully into this question and finds that such an explanation is 

 not feasible. The formation of fresh toxine within an animal's body, apart from the 

 actual presence of the bacteria which ordinarily form it, is unknown, and McFadyean's 

 work — where with the second horse's blood the period of fatal illness was practically 

 the same as with similar quantities of the filtrate from the first horse — I think, 

 clinches the matter. 



Excerpt from a Letter from Br. Eitchic. 



The only objection to the validity of the experiments I think is that it might be 

 a toxine that passes through. I briefly stated [in above notes] an answer to this 

 objection, namely, McFadyean's work, when he inoculated a second horse from the 

 filtered blood of a horse that had itself been infected with filtered blood. Now it 

 might be urged even against this experiment that such a large quantity of poison 

 had been injected into the first horse that even when it had been diluted by all the 

 body fluids of that horse, and had been diminished by excretion for the eight or ten 

 days of the first horse's life, there still remained a large quantity, and it was part of 

 this that killed the second horse. Now if this were the case, there evidently must 

 have been much less given to the second horse than to the first ; and if this were so, the 

 duration of the fatal illness in the second horse would have been much longer. Now 

 this latter did not occur. They both died in about the same time. In fact so different 

 were the doses given in McFadyean's different experiments that if it were a toxine 



' Centralblatt f. Baliter., xxiii. 371. 



- Bulletin dfi la Socictv Centralc de Med. Veterinairc (N.S.), xvii. 441. 



' Jnuo-n. Comparative Path., xiii. 1 ; xiv. 103. 



* Becueil de Mid. Veterinairc, ser. viii., tome viii. 37. 



