241 



the preparation of a medium by digestion of blood with 

 peps i n a n d HC1 followed by filtration, neutralisation, stea- 

 ming, and renewed filtration. By adding the liquid thus pre- 

 pared to agar or broth he obtained media which gave an „ex- 

 cellent" growth of Pfeiffer's bacillus. He found the method 

 practically useless however since the blood solution completely 

 lost its activity after a few days' keeping. 



Fildes however prepared (as stated on p. 229) pepsin-digested 

 blood in 1919 with considerably better results which was su- 

 perior to Cantani's medium by being extremely stable. Can- 

 tani's bad results in this respect presumably depend upon his 

 using pepsin in too small amount (the repeated filtrations indi- 

 cate this), by the absorption of the active substance in the act 

 of filtration, and by the boiling. 



By comparing the statements in the literature about Fildes' 

 and Fleming's media (in connection with my own experiences 

 (see p. 229) one forms the opinion the acid treatment of the 

 blood is sufficient in itself to produce a good growth but that 

 the pepsin causes all the „haemoglobin" to go into solution, 

 and this is the reason a clear solution is obtained without 

 filtration etc. and that on account of the greater content of 

 active substance the solution keeps better. 



Fildes' medium has the same advantage as Fleming's that 

 it becomes sterile even though infected material is used. 



8. Both these media were introduced to supersede Mat- 

 thews' and Mc Intosh's media with trypsin-digested 

 blood, not because they gave unsatisfactory results but because 

 it was desirable to have a medium which was simpler to 

 prepare than these. Fildes' blood solution satisfies this re- 

 quirement in a marked degree, as it is only necessary to 

 prepare a large supply about once a year and ordinary blood 

 from the slaughter-house can be used. 



Media containing trypsin-digested blood, — Gore has also 

 described such a one (cited by Liston) — seem to give an 

 excellent growth of Pfeiffer's bacillus. Both the first-named 

 authors state that trypsin-digested blood also inhibits certain 

 other bacteria, namely Pneumococcus, Streptococcus and va- 

 rious other Gram positive cocci, but not Staphylococcus, con- 

 form bacteria etc. According to Mc Intosh this selective ac- 

 tion is not developed until after digestion has proceeded for a 



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