210 BACTERIA 



raised above the medium, and is of duller lustre. Old colonies 

 become yellowish-brown, the center of which, under a magnifica- 

 tion of sixty diameters, appears darker, and with ravelled edges. 

 On Lb'ffler's blood serum mixture, the organism grows rapidly 

 and well. This and ascites-glycerine-agar culture media are 

 the best for it. Bouillon made from fresh meat is an excellent 

 medium for its growth. The bouillon, which must be alkaline 

 and freshly made, becomes first cloudy; then a fine precipitate 

 settles, and over the surface a delicate pellicle forms. The 

 reaction of the culture presents three types: A, is acid in the 

 beginning, and becomes progressively more acid. B, is alkaline 

 from the start, and progressively more alkaline; this is the most 

 toxic growth. C, acid at the start, becoming alkaline finally. 

 The growth is not so luxuriant as in B, nor is there as much 

 toxin produced. In milk, the growth is luxuriant, without 

 coagulation. The reaction is amphoteric, but in old cultures it 

 becomes alkaline. On potato, rendered alkaline, it will grow, 

 but not characteristically. 



Chemical Activities. No gas is formed, or any curdling or 

 gelatine dissolving ferment. Acids are evolved from sugars; 

 even the sugar found in meat is converted, into lactic acid. In 

 the manufacture of toxin this muscle sugar must be removed. A 

 soluble toxalbumin is created, both in the body and in culture, 

 which is intensely poisonous. See chapter on bacterial products. 



Pathogenesis. Diphtheria in man rneans generally an infec- 

 tion of the mucous membrane of the upper respiratory tract, with 

 the formation of false membranes. The latter may cause death 

 by suffocation. Infection may occur in the skin, vagina, or pre- 

 puce. The toxin not only causes a local necrosis, with the forma- 

 tion of an exudate, consisting of fibrin and leucocytes, but also 

 grave systemic action, with marked degeneration of important 

 nerves and nerve centers, and also of the parenchyma of the 

 kidneys, liver, and heart, paralysis following. In certain struc- 

 tures fragmentation of the nuclei of the cells is noted. Guinea 



