240 



sail solution or broth (9 parts) ond then added lo agar gave 

 I he same good growth as blood heated with the agar; and the 

 uppermost clear portion of the liquid proved to be just as 

 active as the lowest portion containing the clot. That the 

 milieu in which the blood corpuscles (or haemoglobin) are 

 heated, is of considerable importance for its transformation 

 in a favourable direction or the reverse can hardly be doubted. 



If the blood is heated in the agar (or broth) we are on the 

 safe side. There seems to be no particular advantage in heating 

 it separately. 



6. Although Ghon & Preyss found that blood was more 

 deficient as a nutritive substance after simple heating at 100°, 

 he obtained a better result by boiling the blood corpuscles 

 with a solution of sodium carbonate. Later Hundeshagen 

 prepared a medium with blood treated with alkali but renoun- 

 ced it when he became acquainted with heated blood agar. 



Tocunaga has recently devised a medium in the prepara- 

 tion of which blood treated with alkali was also used. Me 

 says that colonies of Pfeiffer's bacillus attain a size of 0.8 

 —1.2 mm. in 24 hours. This must be considered a rather poor 

 growth compared with what can be obtained on the best 

 media 



Media containing alkali -tre a ted blood can therefore 

 be used but are not among the best. 



Considerably belter growth occurs when the blood is treated 

 with strong mineral acids. Fleming (1919) introduced 

 this method; he mixed blood with the same volume of normal 

 HC1 or H 2 S0 4 . A brownish liquid with a brown precipitate 

 was obtained. After standing some minutes it was neutralised 

 with NaOH. The deposit was removed by decantation or cen- 

 trifugation and the clear liquid used to mix with agar. This 

 method had the advantage that a sterile medium was ob- 

 tained even though the original materials were grossly infected. 

 Wyard and Skajaa found that this medium could be used but 

 from their descriptions it appears that it did not always pro- 

 duce a good growth, and that the blood solution itself as 

 well as the final agar would only keep for a few days. 



Neither alkali treatment nor acid treatment seems therefore 

 to give media that can be specially recommended. 



7.. In 1901 Cantani (1) reported experiments dealing with 



