PROTECTIVE INOCULATIONS. 367 



appear smaller, the structures of the eye become clearer, the inoculation 

 wound is but a bluish fibrous scar, until in from six to twelve weeks, in suc- 

 cessful cases, all irritation has disappeared and the eyes present, as in the 

 animals I now show you, but fibrous evidence of the traumatism and the in- 

 flammatory processes which have been set up by the inoculation. In all the 

 controls, as you see, the inoculation wound is cheesy and the cornea and iris 

 are more or less destroyed by tubercle and cheesy areas. 



"Some of the protected animals slowly relapse, and the one I now show 

 you has small tubercles growing- on the iris; but even in such eyes the 

 entire absence of caseation is noticeable, and the disease progresses almost 

 imperceptibly. I have repeated this experiment on three sets of rabbits with 

 about the same results each time. The vaccinations as practised are of them- 

 selves, in some instances, fatal : but the fact remains that where recovery 

 takes place a marked degree of immunity has been acquired. I do not lay 

 any claim, therefore, to have produced a complete or permanent immunity 

 by a safe method, but it seems to me that these eyes constitute a scientific 

 demonstration of the fact that in rabbits preventive inoculation of bird- 

 tubercle bacilli can retard, and even abort, an otherwise progressive localized 

 tubercular process so completely as to prevent destruction of the tissues 

 threatened, and that the future study of anti-tubercular inoculation may not 

 be as entirely hopeless as it has until recently appeared." 



TYPHOID FEVER. 



Brieger (1885) found in cultures of the typhoid bacillus small 

 amounts of volatile fat acids, and when grape sugar has been added 

 to the culture medium lactic acid. He also obtained a highly alka- 

 line basic substance possessing toxic properties which he named 

 typhotoxin (C 7 H 17 NO 2 ). This he supposes to be the specific product 

 to which the pathogenic action of the bacillus is due. It produces in 

 mice and guinea-pigs salivation, paralysis, dilated pupils, diarrhoea, 

 and death. 



More recent experiments by Pfeiffer (1894) lead him to conclude 

 that the specific poison of the typhoid bacillus is not present in fil- 

 tered cultures, but is closely associated with the bacterial cells. Ac- 

 cording to Pfeiffer the bacillus may be killed by a temperature of 54 C. 

 without injury to this toxic substance. The fatal dose of the dead 

 bacilli is from three to four milligrammes per one hundred grammes 

 of body weight for guinea-pigs. Susceptible animals may be im- 

 munized by means of this toxic substance, and their blood is found to 

 contain an antitoxin which has a specific bactericidal action upon the 

 typhoid bacillus. But, according to Pfeiffer, the blood serum of ani- 

 mals immunized in this way does not differ from normal serum in 

 its action on bacillus coli communis and other species of bacteria. 

 These results are believed, by the author referred to, to settle the 

 question of the specific character of the typhoid bacillus, and to dif- 

 ferentiate it from nearly allied species. The presence of a typhoid 

 antitoxin in the blood serum of individuals who have recently suffered 

 an attack of typhoid fever has also been demonstrated by Pfeiffer. 



