VITA LITYPA THOGENESIS. 24 1 



Bouillon is first clouded, and then the growth gradually 

 accumulates on the sides and bottom of the tube in the shape 

 of a light flocculent precipitate, leaving the bouillon clear 

 and transparent. Not infrequently the surface of the medium 

 is covered by a very thin, fragile membrane. Picking up 

 the tube without more than the ordinary agitation caused 

 thereby causes the membrane to fall to pieces. 



On alkaline potato a delicate surface coating is formed. 

 The organism grows in milk without changing its appearance. 

 Litmus mill: is first turned a faint red, and then blue again. 

 The bacillus grows well on both raw and boiled eggs. 



Vitality : A striking characteristic of the diphtheria bacil- 

 lus is its very feeble resistance to heat and chemicals. It 

 is destroyed by a temperature of 58 C. in ten minutes; by 

 1:1000 solution of bichloride in twenty seconds, and as 

 rapidly by 5 per cent, solution of potassium permanganate, 

 5 per cent, carbolic acid, 3 per cent, carbolic acid in 30 per 

 cent, alcohol, and 4 per cent, cresol in 40 per cent, alcohol. 

 Pure lemon juice is rapidly fatal. It cannot withstand dry- 

 ing for any length of time, but will remain alive for months 

 if enclosed in a shred of the diphtheritic membrane. It is 

 not affected by cold. 



Pathogenesis : The diphtheria bacillus is pathogenic for 

 man as well as animals, especially cats, chickens, and pigeons. 

 Animals are frequent sources of infection, particularly when 

 they are petted. The organism gains entrance to the throat, 

 and when conditions are favorable for its development it pro- 

 duces the characteristic pseudomembrane of diphtheria. Other 

 varieties of diphtheria, as well as chemicals, not infrequently 

 are the cause of the formation of a pseudomembrane in the 

 throat which cannot, by its appearance, be differentiated from 

 the diphtheritic membrane. This membrane usually is formed 

 on the fauces first, but may appear first in the pharynx, nares, 

 larynx, or on the tonsils. In rare instances the membrane 

 may be formed in the vagina or rectum, on the conjunctiva, 

 or in a wound of the skin. This membrane has a dirty white 

 or grayish color suggestive of decomposition, and when it is 

 forcibly detached it leaves a raw, bleeding surface. 



The diphtheritic infection, like tetanus, is purely a local one. 



16 Bact. 



