THE TUBERCLE BACILLUS 99 



destroyed, centrifugalize and wash the sediment with sterile water, spread on 

 slides, stain and mount. 



Examination of pleura! and other effusions and pus: centrifugalize and make 

 spreads from sediment, dry, stain and examine or inject the entire sediment 

 into the peritoneal cavity of a guinea-pig. 



Microscopic examination of these fluids seldom reveals tubercle bacilli 

 even when the tubercle bacillus is the 'cause of their formation. When injected 

 into guinea-pigs 50 per cent, or more fail to produce tuberculosis. 



Examination of Milk. -Centrifugalize i pint until cream separates. Remove 

 the cream, dissolve it in ether, centrifugalize the ether, wash the sediment in 

 sterile water and inject it into a guinea-pig, intraperitoneally. 



Centrifugalize the skimmed milk until sedimentation is complete and inject 

 the sediment into a second guinea-pig. 



Examination of Feces. Give the patient a dose of salts the night before 

 sample is collected. Add antiformin to the stool and allow it to digest for 12 

 hours, collect and wash the sediment, inject a couple of cubic centimeters sub- 

 cutaneously into a guinea-pig and make smears from the sediment for micro- 

 scopic examination. 



DIFFERENTIATION OF 



Human, Bovine and Avian types of tubercle bacilli. Recent disclosures sug- 

 gest that when microscopic examinations of sputum, urine, feces, milk, etc., fail 

 to show tubercle bacilli in suspected cases, cultural tests may do so and it now 

 seems advisable to make such tests. The author has had most promising re- 

 sults with the methods recommended by Petroff, with both Petroff 's medium 

 and (William's and Burdick's) modification. They all show practically the 

 same staining characteristics. 



Petroff's Method. Mix equal parts of sputum and 3 per cent, sodium hydrox- 

 ide solution and incubate at 37C. for ^ hour. Add normal HC1 until neutral 

 to litmus paper (litmus paper used should be sterile). Centrifugalize at high 

 speed for 15 minutes. Pipette off supernatant fluid and plant sediment on 

 Petroff's medium or (William's and Burdick's) modification. Incubate tubes at 

 37C. If growth does not appear in 2 weeks examine microscopically as it is fre- 

 quently present but invisible from the fifth to the fifteenth day. 



Observed in tissue the bovine bacillus is shorter and thicker and more uniform 

 in size and staining than the human; the avian longer and relatively more 

 slender, but these differences in size and shape are usually so modified by 

 cultivation on artificial media as to make microscopic differentiation frequently 

 uncertain or impossible. 



The human, type grows more rapidly and luxuriantly on culture media than 

 the bovine. In acid glycerin bouillon the human type causes slight if any 

 reduction of the acidity during the early weeks of cultivation, later it makes 

 the medium more acid; the bovine type reduces the acid reaction to or near 

 the neutral point and does not increase acidity later. 



