BUKEAU OF ANIMAL INDUSTRY. 363 



the disease. This fundamental information enabled investigators to 

 apply themselves to a line of study which resulted in the compre- 

 hensive knowledge now at our command concerning the pathogenesis 

 of the affection. The practicing veterinarian has no longer to fear 

 the development of this dreaded disease subsequent to operative or 

 traumatic wounds, as he is assured protection for his patients by the 

 injection of a preventive dose of tetanus antitoxin. It is regrettable, 

 however, that this method of prophylaxis, which to-day is probably 

 the most certain in preventive medicine, is not used to a more general 

 extent, es^Decially in localities where the disease is very prevalent. 



In a series of expermients on horses recently undertaken by the 

 buTeau it was aimed to establish the smallest quantity of antitoxin — 

 that is, the minimum number of units — which would protect a horse 

 against a positive infection of tetanus. The preliminary experi- 

 ments were carried out on guinea pigs, and after establishing the 

 best procedure of introducing the infection into the system, experi- 

 ments were undertaken on horses. The animals were infected with 

 the pure cultures of tetanus spores and bacilli from which the toxins 

 were eliminated by either washing the cultures or heating to 75° C. for 

 45 minutes. In infecting the horses the natural modes of infection 

 were followed as closely as possible. Thus the virus was introduced in 

 artificially-punctured wounds of the foot, into bruised, lacerated., 

 trauHuitic wounds of the body, into the scrotum, etc. In all instances 

 a small quantity of sterilized dirt was mixed with the culture, which 

 was foimd in the preliminary experiments on guinea pigs to be essen- 

 tial in producing a positive fatal infection. After infecting the 

 horses, each animal after varying lengths of time received subcu- 

 taneous injections of antitoxin in varying quantities. 



The results showed that 500 units of tetanus antitoxin injected 

 even 96 hours subsequent to the infection will protect an animnl 

 against the disease. In no instance did an}' signs of tetanus develop 

 in the animals after receiving over 400 units of antitoxin, while the 

 animal used for a check and those receiving very small quantities 

 of antitoxin succumbed to the artificial infection. Symptoms of 

 localized tetanus developed in the horses which received 250 and 400 

 units, but even these animals recovered. 



In consideration of the fact that all the horses used in these tests 

 were quite aged and accordingly not nearly so susceptible as young 

 animals, a somewhat larger quantity of antitoxin would be necessary 

 to prevent absolutely the development of tetanus in the latter ani- 

 mals. Accordingly 500 units would seem to be sufficient for the pre- 

 vention of tetanus in horses of any age. These results are of great 

 interest when it is considered that the cost of the antitoxin for 

 immunization can be greatly diminished by employing with safety 

 only one-third of the quantity of antitoxin which is now being used 

 for protective purposes. 



In these experiments it will be observed that the antitoxin was 

 employed at different periods subsequent to the infection, and the 

 results obtained indicate that the administration of the antitoxin 

 even OG hours after the infection will prevent the development of 

 the disease. This is of considerable practical importance, inasmuch 

 as frequently the veterinarian is called to attend to an injured animal 

 only after a consideral)le time has elap.sed following the injury. 



