QONOOOCCUS. 291 



obtain the necessary amount of human blood that is to 

 be smeared over the surface of the slanting agar-agar 

 when Pfeiffer's method is employed. 



Wright's modification of Steinschneider's method has 

 given such satisfactory results in his hands that it will 

 be given here somewhat in detail. The medium con- 

 sists of a mixture of urine, blood-serum (human or 

 bovine, either serving the purpose), and nutrient agar- 

 agar. The urine and blood-serum are collected with- 

 out special aseptic precautions, and subsequently freed 

 from bacteria by filtration through unglazed porcelain. 

 Frequently this is the tedious part of the process, as 

 the serum and urine pass very slowly through the 

 porcelain filters generally employed in laboratories. 

 Wright recommends a filtering cylinder manufactured 

 by the Boston Filter Company as an apparatus that not 

 only gives a sterile filtrate, but also permits of very 

 rapid passage of the fluid. 



The details of the method as given by Wright are as 

 follows : " A litre of nutrient agar is prepared in the 

 usual manner, and after filtration it is evaporated to 

 about 600 c.c. This concentration is desirable, so that 

 after dilution with the urine and serum the medium 

 may be sufficiently firm. This concentrated agar is then 

 run into test-tubes and the whole sterilized by steam on 

 three successive days. The quantity of agar placed in 

 each tube is smaller than is usual ; this is in order to 

 allow for the subsequent addition of the urine and 

 serum. 



" The blood-serum, which need not be free from cor- 

 puscles, is first passed through white sand, which is 

 supported in a funnel by filter-paper, in order to re- 

 move as far as is possible any particles in suspension, 



