THE TUBERCLE BACILLUS. 325 



Summary of the method given: 



Cover-glass preparation. Dilute alcohol (60 per cent.). 



Dry in air. Wash in water. 



Fix in flame. Methylene blue (i - i min. ). 



Carbolic fuchsin, hot, (1-2 min.). Wash in water and examine. 



Wash in water. Dry in air. 



Dilute nitric acid (10-15 seconds). Mount in balsam. 



The sputum should be collected in the morning immediately 

 after rising, inasmuch as at this time it is likely to be rich in bac- 

 teria. It may be necessary at times to instruct the patient that 

 sputum, and not saliva, is what is wanted. The material should be 

 poured into a wide glass dish, such as that of Petri, and examined for 

 the presence of yellowish particles. These are portions of the 

 caseous matter from the lungs and are likely to be rich in bacteria. 

 The sputum should be examined also for elastic fibers, and the pres- 

 ence of streptococci and of other bacteria should be noted (mixed 

 infection). 



Suspected urine should be centrifugated and the deposit 

 examined in the same way as indicated above. In the case 

 of milk, it is advisable to centrifugate and then to inject 

 the combined cream and sediment into guinea-pigs. 



Occasionally sputum, pus, or other products of disease 

 will not reveal the tubercle bacillus by this method. 

 Either the germ is present in a spore-like condition, 

 or it is present in very small numbers and thus escapes 

 detection. In such a case it is necessary, as with urine or 

 milk, to resort to an animal experiment in order to estab- 

 lish the diagnosis. For this purpose some of the material 

 is injected into the peritoneal cavity of a guinea-pig. In 

 three or four weeks the animal is killed, and if, on post- 

 mortem examination, tubercular nodules are found in the 

 abdominal cavity they should be examined for the tubercle 

 bacillus. A portion of the cheesy matter fromithe inside of 

 the nodule should be used for the examination. Cultures 

 may be made as indicated on p. 315. 



Pathogenesis. — Man, monkey, cattle, horse, ass, hog, goat, par- 

 rot, guinea-pig, field mouse, rabbit, and cat are susceptible. White 



