2 4 o POPULAR SCIENCE MONTHLY 



In the vaccinated animals, on the contrary, the introduction of the 

 mammalian bacilli at once gives rise to a marked degree of irritation. 

 From the second to the fifth day the vessels of the conjunctiva become 

 engorged, and evidences of marked inflammation appear in the anterior 

 chamber and on the iris (reaction of immunity). However, at the end 

 of the second to the third week, when the eyes of the controls begin to 

 show progressive and steadily increasing evidence of inflammatory re- 

 action, the irritation in those of the vaccinated animals begins slowly 

 to subside and the eyes to mend. In from six to twelve weeks, in the 

 successful cases, all irritation has disappeared and the eyes present 

 only the evidences of traumatism and inflammation. This experiment 

 leaves no doubt of the protective influence exerted by the first inocula- 

 tions of the avian bacilli and clearly establishes that related cultures 

 of tubercle bacilli of moderate virulence for an animal species, can 

 afford protection to subsequent inoculation with special and more patho- 

 genic strains of the bacillus. Notwithstanding the fact that, as Dr. 

 Trudeau records, some of the protected animals slowly relapse and 

 the disease resumes its progress, although by almost imperceptible 

 stages, the experiment still shows that protection, not absolute immu- 

 nity, from tuberculosis may be obtained in rabbits by a species of 

 vaccination. 



De Schweinitz in 1894 reported certain experiments which he made 

 on guinea-pigs and cattle. He inoculated the former with a culture 

 of tubercle bacilli of human origin cultivated for about twenty genera- 

 tions in broth. This culture was of a low grade of virulence for these 

 animals, but it served to protect them to such an extent that when 

 they were afterwards inoculated with tuberculous material from a cow 

 they remained healthy, while control pigs injected with the same 

 material became tuberculous and succumbed in about seven weeks. De 

 Schweinitz injected large quantities of human tubercle bacilli into 

 cattle — beneath the skin, into the peritoneal cavity and into the circu- 

 lation — without injury. 



I may, at this time, digress for a moment and leave the more 

 strictly chronological method of presentation, to allude to the set of 

 experiments on the protection of guinea-pigs from tuberculosis, which 

 Trudeau reported to the National Tuberculosis Association at its last 

 meeting. The special merit of this experiment is that it shows the ex- 

 istence of a connection between virulence and infectivity in the germ 

 and its capacity to confer immunity. Unless the bacillus has the power 

 to gain some foothold in the body it affords no protection ; if on account 

 of high pathogenic power or virulence, it easily gains a foothold, then 

 it brings about infection. To choose a culture of tubercle bacilli of 

 just the right grade of virulence is one of the conditions, apparently, 

 of successful experiment, as it must also be, in view of this fact, one 



