104 ESSENTIALS OF BACTERIOLOGY. 



method of Gram can be used, but the better way is to use the 

 following : 



Carbol-fuchsin, 15 to 30 minutes. 

 5 per cent, sulphuric acid, 1 minute. 

 Alcohol, until a light-red tinge appears. 

 Weak methylin blue, 3 to 5 minutes. 

 Alcohol, for a few seconds. 

 Oil of cloves, until cleared. 

 Canada balsam, to mount in. 



Instead of carbol-fuchsin, alcoholic solution offuchsin or aniline 

 water fuchsin can be used, but the sections must remain in the 

 stain over night. 



Hardened sputum and sectioning. Sputum can be hardened by 

 placing it in 98 per cent, alcohol. Thin sections can be obtained 

 by imbedding the hardened sputum in collodion. The sections 

 are then stained as ordinary tissue sections. 



To preserve sputum. Sputum can be preserved for future use 

 by placing it in alcohol, where it can be kept for months. Cover- 

 glass preparations can then be made by softening the coagula 

 with a small amount of liquor potassa. 



The resisting action of the bacillus to acids is supposed to 

 be due to a peculiar arrangement of the albumen and cellulose 

 of the cell rather than to any particular capsule around it. 



Pathogenesis. When a guinea-pig has injected into its peri- 

 toneal cavity some of the diluted sputum containing tubercle 

 bacilli it perishes in about three weeks, and the following 

 picture presents itself at the autopsy : at the point of inoculation 

 a local tuberculosis shmos itself, little tubercular nodules contain- 

 ing the characteristic bacilli. In the lungs and the lymphatics, 

 similar tubercles are found, a general tuberculosis. 



If the animal lingers a few weeks longer, the tubercles become 

 necrosed in the centre and degeneration occurs, the periphery 

 still containing active bacilli, cavities having formed in the 

 centre. 



Since the bacilli die in course of time, killed by their own pro- 

 ducts, their number forms no correct guide of the damage present. 

 Even their absence in the sputum does not preclude the ab- 

 sence of a tubercular process. It is their presence only that 



