Nc. 6. DEPARTMENT OF AGRICULTURE. 321 



creased. Rabbits were not killed by sub-cutaiieons inoculation. 

 Guinea-pigs died after an average of forty-two and one-tliird days. 

 A calf inoculated intiaperitoneally showed no ill effect and gave no 

 reaction to tuberculin after seven weeks. 



Culture Nasua Xarica (Coati) of Theobald Sniilli, inclosed in collo- 

 dion sacs, was kept iti the peritoneal cavity of a 3earliug heifer for 

 eleven months. On removal there was considerable increase in the 

 growth, especially in one sac. Cultures were recovered from the 

 sacs, and showed some marked changes, especially in manner of 

 growth. On both blood-serum and glycerin agar, the growth was 

 most rapid, at least twice as rapid as usual for this cullure. On 

 serum it covered the surface in seven to ten days, as a thick, white, 

 moist layer, almost cottony near the water at bottom. On glycerin 

 agar the growth was more dry and wrinkled, but very rajjid. The 

 bacilli stain more evenly, and are on the whole shorter, though long 

 forms are seen. Guinea-pigs a«d rabbits inoculated subcutaneously 

 are still alive after four months. A calf which received 4 c. c. of a 

 milky suspension in (he jugular vein reacted to tuberculin after ten 

 weeks. 



The experiment is being co«itinued, the culture recovered from the 

 capsule having been placed again in the peritoneal cavity of another 

 calf. 



No conclusions can be drawn as yet, though the indications are 

 that both cultures have become less strictly parasitic rather than 

 more so, by the procedure. 



Interpretation of Results,- — Accepting it as proven that the bovine 

 tubercle bacillus has, as a rule, considerably greater pathogenic 

 power than the human bacillus for a large majority of experimental 

 animals, how should we interpret this in regard to man? Is it fair 

 to conclude that this increase of virulence will hold good for man 

 also? Until the contrary is proven, or until good reason for believ- 

 ing the contrary is shown, it is in my judgmeiit right that this con- 

 clusion be held, at least as a working hypothesis. I am aware of 

 the objections to this view that will be raised by some, and acknowl- 

 edge freely that it cannot be accepted as conclusive. Virulence is, 

 no doubt, a factor which is relative to the subject, and exaltation of 

 virulence for one species does not necessarily prove an increased 

 virulence for other species. Indeed, the reverse is true in some in- 

 stances.* However, it cannot be denied, as a general rule, that 

 when the virulence of a jyathogenic organism is increased for one 

 animal it is increased for all that are naturally susceptible to its 

 action. 



The tubercle bacillus is unique in the extent of its pathogenic 

 activity, both by direct experimental inoculation as well as by infec- 



*The streptococcus is said to become increased in virulence for mice by 

 successive passages through these animals, but less virulent for rabbitp. 



21—6—1901 



