90 BACTERIOLOGY. 



through a cork in the top of the apparatus, if the large 

 form of apparatus is used ; or should lie upon a rack of 

 cork or wood, its bulb being free and a little lower than 

 the other extremity, if the small, old-fashioned appa- 

 ratus of Koch is employed. The latter form is prefer- 

 able, as it is more easily managed. 



When solidification is complete, the tubes are to be 

 retained in the erect position and, unless they are 

 intended for immediate use, must be prevented from 

 drying. The superfluous ends of the cotton plugs should 

 be burned off, and the mouths of the tubes may then be 

 covered by sterilized rubber caps, or, as Ghriskey sug- 

 gests, they may be closed with sterilized corks pushed 

 in on top of the cotton plugs. Even with the greatest 

 care it not uncommonly happens that one or two of the 

 lot of tubes thus prepared and protected will become 

 contaminated. This is usually due to spores of moulds 

 that have fallen into the rubber caps or on the cotton 

 plugs during manipulation, and, finding no means of 

 outward growth, have thrown their hyphse downward 

 through the cotton into the tube, and their spores have 

 fallen on the surface of the serum and developed there. 



It is often desirable to obtain blood-serum in small 

 quantities, either for culture purposes or for the study 

 of the serum of different animals in its relation to bac- 

 teria, and for this purpose Nuttall {Centralbl. Bakt. u. 

 Parcmtenkunde, 1892, Bd. xi. p. 539) suggests a very 

 convenient method. By the use of a sterilized vessel, 

 of the shape given in Fig. 17, from ten to one hundred 

 cubic centimetres of blood can be collected, and if proper 

 precautions are observed no contamination by bacteria 

 need occur. The collecting bulb is used in the fol- 

 lowing way : An artery, either femoral or carotid, is 



