^Bfcreater chance of obtaining satisfactory data if we direct our atten- 

 uation to some analogous disease attacking one of the lower animals. 

 Such a disease we have in Texas fever, occurring in the Bovidae, 

 as the result of the action of an animal parasite, Piroplasma 

 higeminiim, which invades the red blood corpuscles much as Laveran's 

 parasite invades those of the human subject. 



As mentioned in the preceding chapter, Smith and Kilbome 

 and Koch have demonstrated that the Bovidae may acquire a 

 real immunity against Texas fever. Nicolle and Adil Bey^ at [293] 

 Constantinople found indigenous races that exhibited a remarkable 

 immunity against the Piroplasma. Having demonstrated this fact 

 the idea occurred to them to inoculate these refractory cattle with 

 very large quantities of virulent blood and to make use of the serum 

 from animals so treated for the prevention of infection in susceptible 

 races of Bovidae. This experiment gave negative results. Ligniferes^ 

 elaborated a special method of vaccinating susceptible Bovidae and 

 was successful in obtaining very encouraging results. A commission 

 of veterinary surgeons from Alfort^ appointed to verify these observ- 

 ations came to the conclusion that "the vaccination as carried out 

 by Ligniferes was absolutely effective." 



Ligniferes also carried out researches on the protective power of 

 the blood serum of his immunised cattle. In a communication to 

 the International Congress of Medicine, held in Paris in 1900, he 

 stated that the injection of several hundred cubic centimetres of this 

 fluid did not protect normal animals against infection. We must 

 conclude, therefore, that, here also, we have another example of 

 acquired immunity unaccompanied by the presence of any protective 

 property of the blood fluid. 



These results have received confirmation from a most authoritative 

 source. Nocard has kindly communicated to me the fact that he has 

 tried in vain to confer immunity on normal dogs into which he has 

 injected blood serum coming from dogs that had recovered from the 

 disease produced by a haematozoon closely allied to that of Texas 

 fever or serum from sheep immunised with blood from the affected 

 dogs. 



Looking at the data we have just summarised as a whole, we are 



1 Ann. de VInst. Pasteur., Paris, 1899, t. xiii, p. 343. 



2 "La 'Tristeza' ou Malaria bovine dans la Republique Argentine," Buenos 

 Ayres, 1900, p. 142. 



3 Bull. Soc. centr. de med. veterin., Paris, 1900, seances des 12 et 26 juillet. 



