394 ACTINOMYCETES. 



by transition forms. Young cultures usually present 

 delicate, old ones thick pellicles. 



Alkaline bouillon first becomes acid, then alkaline 

 again, the latter change being favored by passing air 

 through it. (See Chemical Activities. ) The diphtheria 

 bacilli grow poorly upon bouillon which has been long 

 stored, and in such a case the nutrient value is increased 

 by boiling it (Escherich). 



Milk. — Luxuriant growth usually occurs without coagu- 

 lation. They live a long time. Reaction amphoteric. 

 According to Schottelins, this is especially true of raw 

 milk, cooked milk being much less favorable (Q,. B. xx, 

 897). 



Potato. — Upon acid potato very poorly or not at all; 

 upon alkaline potato after eight to fourteen days, a very 

 scanty growth. It appears only as a delicate, shining, 

 sharply limited veil, which sometimes may be lifted with 

 a platinum needle. A more luxuriant growth of the 

 diphtheria bacillus upon potato occurs, although only 

 rarely (58, ix). 



Special Nutrient Media. — In non-albuminous urine (Guinochet) 

 which has been sterilized and rendered faintly alkaline the diphtheria 

 bacillus grows slowly, but it is pathogenic. Schloffer (C. B. xiv, 657) 

 recommends urine-agar (a meat infusion-peptone agar — 2% — is mixed 

 with fresh, sterile urine). According to Gamaleia, a good nutrient 

 medium contains glycerin, 40 parts; meat extract, 5 parts; sodium 

 chlorid, 5 parts; and water, 1000. 



Spore-formation does not occur. 



Viability. — (a) In the body : It is found in the throat 

 for weeks or even for two months after convalescence from 

 diphtheria in many cases (Loffler, Abel). 



(6) In cultures : If kept cool and in the dark, for from 

 six months to one and one-half years. In the incubator 

 they usually die after one to three months because of 

 drying. In well-closed bouillon cultures they remain 

 alive also in the incubator for one year or longer. 



(c) In water and foods : See Montefusco (C. B. xxi, 352). 



Resistance to : (a) Drying : Very considerable. Pure 

 cultures on silk threads in the room remain alive three or 

 four weeks, and under favorable conditions for months. 

 In dried diphtheria membranes they live as long as three 



