VACCINE-THERAPY 111 



to a septic metritis developing into a septicaemia, and lead- 

 ing up to a specific arthritis. One or more joints may be 

 involved. The stifle, by reason of its large capacity, and 

 probably its nearness to the centre of infection, is, in the 

 writer's experience, particularly singled out for bacterial 

 invasion. 



Of course one sees many cases in practice where the 

 placenta is retained for a long period, and very septic, 

 germ-laden discharges are evacuated, perhaps for weeks, 

 and yet no arthritic lesions develop, nor may we find any 

 indications whatever of septic infection or intoxication; 

 while, on the contrary, the placenta may be retained only 

 a few days, or there may only be slight bruising of the 

 genital passage, and septicaemia and septic arthritis de- 

 velop. We can only explain these extreme conditions by 

 stating in the one case the bacteriotropic forces were in 

 themselves capable of acting as a resisting barrier against 

 a systemic bacterial invasion, and in the other they were 

 not. So far as our present knowledge goes, it would 

 appear there exists in the blood-serum a specific opsonin 

 for all or nearly all pathogenic bacteria ; thus, we may have 

 an antistaphylococcal opsonin, an antistreptococcal op- 

 sonin, an anticolic opsonin, and so on. The quantity of 

 opsonin differs in various animals, and even in the same 

 animal at different times ; therefore an animal may be, and 

 is, more resistant to bacterial invasion at one time than at 

 another. 



This variation is dependent upon many and varied causes, 

 which in themselves are chemically complex and difficult to 

 understand. 



But if we do not know why these opsonins and other 

 antibodies diminish in quantity as they do, we do know 

 how to raise them to a standard of proficiency, and so 

 prepare the antibodies to clear the system of offensive 

 bacteria — i.e., by using a suitable vaccine or serum, or both 

 combined. 



Where an animal has a high temperature, is off its 



