237 



He found that blood thus heated was superior to blood hae- 

 molysed in various other ways. 



According to Auerbach (1904) the agar should be 60° — 70° 

 when it is added to the blood (pigeon). The colonies of Pfeif- 

 fer's bacillus then attained a diameter of 1 mm. which was 

 then reckoned a good growth. Curiously enough he states that 

 the medium is impaired when the agar is made so hot that 

 the blood is tinted brown. None the less it was precisely by 

 means of this further heating that the best and most commonly 

 used media for Pfeiffer's bacillus were subsequently obtained. 

 This step forward was made by Cohen & Fitzgerald in 1910. 

 As it seems to be so little known (compare Coca & Kelley) that 

 this was the first contribution on the preparation of the ty- 

 pical „chocolate agar" the method will be given word for 

 word: „on fait fondre en le portant a 1' ebullition un tube de 

 gelose peptonee; on le refroidit a 60° environ, puis on in- 

 troduit dans le tube lc.c. de sang de lapin defibrine; on melange 

 de facon intime le sang a la gelose en roulant le tube entre 

 les mains, puis on le plonge dans un bain-marie chauffe a 

 80°; on l'y laisse durant trois minutes; le sang est cuit et le 

 milieu prend une consistance plus epaisse de teinte brun cho- 

 colat". Pfeiffer's bacillus however must have been trained 

 to this medium before „on constate que la culture presente 

 l'aspect non plus de fines gouttelettes translucides, mais bien 

 d'une couche epaisse, uniforme, de coloration grise, de consi- 

 stance cremeuse: l'abondance de cette culture rappelle celle 

 du staphylocoque sur agar peptone". 



In 1912 Povitzky (cited from Coca & Kelley) made the 

 same discovery of the value of „chocolate blood" as a nutritive 

 medium. In 1915 Hundeshagen learnt this method and intro- 

 duced it into Germany. Lloyd (1916) added to agar (accor- 

 ding to Douglas or Cole & Onslow) 5»/o ox blood, heated 

 in steam at 100° for 3/ 4 hour, the clot removed by centrifuging 

 or filtering through glass wool, and finally sterilised at 100°. 

 She recommends this medium for the cultivation of Pfeiffer's 

 bacillus, Meningococcus, Pneumococcus etc. without a further 

 description of the conditions of growth. 



Nevertheless Levinthal (1918) independently of the pre- 

 vious authors again discovered by a roundabout method the 

 value of strongly heated blood agar as a nutritive medium. 



