PROTECTIVE INOCULATIONS. 345 



"5. Still greater resistance irregular lesions in the form of abscesses, 

 subcutaneous and subperitoneal. 



4k 6. Nearly complete immunity very slight reaction at the point of in- 

 oculation." 



Up to the year 1894 the bacteriological experts of the Depart- 

 ment of Agriculture had not proposed to make a practical application 

 of the facts developed in their experimental work in the way of pro- 

 tecting herds of swine by means of inoculations with an attenuated 

 virus, or with sterilized cultures. In the report on swine plague, 

 made by the Bureau of Animal Industry published in 1891, the fol- 

 lowing measures for arresting an epidemic are recommended : 



"When the disease has actually appeared in a herd the question generally 

 arises whether it is worth while to make any attempt to save a portion of the 

 herd or to leave them to their fate. As a rule it may be stated that it is best 

 to slaughter both healthy and diseased at once, and give the surroundings 

 sufficient time to rid themselves of the infection before fresh animals are 

 brought into them. If this be not desirable, we should recommend the fol- 

 lowing measures to be vigorously carried out : 



"a. Removal of still healthy animals to uninfected grounds or pens as 

 soon as possible. 



" b. Destruction of all diseased animals. 



" c. Careful burial or burning of carcasses. 



"d. Repeated thorough disinfection of the infected premises. 



"e. Great cleanliness both as to surroundings and as regards food." 



In the same report (1891) the following reference is made to pro- 

 tective inoculations : 



" As regards swine plague the experiments which have thus far been car- 

 ried out indicate that this disease may prove amenable to preventive inocula- 

 tion. We have been able, by the injection of both living cultures and those 

 sterilized at a low temperature (58 C.), to make the most susceptible animals 

 rabbits insusceptible to the most virulent swine plague bacteria. By two 

 subcutaneous injections of cultures of swine-plague bacteria, swine have 

 been made insusceptible to doses injected into the circulation which proved 

 fatal to control pigs within twenty-four hours." 



According to Smith the experiments of Metchnikoff (1892), re- 

 ported as made with the bacillus of hog cholera, were in fact made 

 with the bacillus of swine plague ; we therefore refer to them here. 

 These experiments showed that rabbits could be easily immunized 

 against the pathogenic action of virulent cultures by means of blood, 

 from an infected animal, sterilized by heat. Doses of 1.5 cubic centi- 

 metres, or more,* were fatal to rabbits; but smaller doses, repeated 

 several times, given either subcutaneously or by injection into the 

 circulation, caused the animal to become immune. 



STREPTOCOCCUS INFECTION. 



It is now generally recognized by pathologists that erysipelas, 

 puerperal fever, certain forms of diphtheritic inflammation of the 



