236 



growth of Pfeiffer's bacillus and partly to make it easier to 

 recognise by means of the characteristic symbiosis phenomenon. 

 (Brown & Okcutt, Roos). Harvey, Brown, & Cunningham 

 cultivated Pfeiffer's bacillus on blood agar for the preparation 

 of vaccine, in association with Pneumococcus and Strepto- 

 coccus, which increased the growth of Pfeiffer's bacillus con- 

 siderably while the growth-promoting organisms always kept 

 in the background. 



Savini & Savini-Castano employed growth-promoting bac- 

 teria even in the preparation of the medium. A mixture of 

 glycerin and Staphylococcus culture was kept at 58° — 60° over- 

 night, after which blood was added and the mixture allowed 

 to stand an hour at 56° — 58°. The blood corpuscles are hae- 

 molysed by the glycerin; the solution thus produced which is 

 said to keep for months, is added to agar or broth. The co- 

 lonies that grew on it were „riesengross". It is doubtful 

 whether this medium can compare with the mOre modern 

 ones. The reason for dwelling upon it is that several different 

 factors, each active in itself are made use of in its preparation: 

 growth-promoting bacteria, haemolysis, and heating. 



Whether the glycerin, which is frequently added to the 

 media containing heated blood mentioned below, plays any 

 important part I have been unable to find out According 

 to Wolf it was of no importance in the symbiotic growth on 

 ordinary agar. 



5. Although agar containing heated blood was not used 

 on a large scale prior to the last few years the first time such 

 a medium was employed dates as far back as 1894 when 

 Voges prepared his haemoglobin medium by putting some 

 drops of human blood in a Petri plate and pouring melted agar 

 at 100° over them whereupon the contents were well mixed. 

 A transparent, light red medium was thus obtained. That the 

 blood kept its red colour is intelligible as the agar was na- 

 turally instantaneously cooled to a considerable extent by con- 

 tact with the glass plate. Voges pronounced this medium better 

 than any hitherto known. Grassberger (2), who on the basis 

 of Voges' contribution in 1898 employs a similar method of 

 procedure points out the importance of the agar being hot. An 

 hour's heating at 50°— 60° was however adequate to bring forth 

 the desired improvement of its value as a nutritive medium 1 . 



