METHODS OF CULTIVATION. 161 



cies contained in it will depend upon the use of a 

 suitable culture-medium, and the maintenance of 

 favorable conditions as to temperature and a suf- 

 ficient supply of oxygen, if required. 



Natural Culture-Fluids. The natural culture- 

 fluids which are available for use are blood, milk, 

 urine, and aqueous humor from the eye of one of 

 the lower animals. 



All of these have been used, and all may be 

 obtained in a pure state from the living animal by 

 adopting proper precautions. 



Blood. The observations of numerous experi- 

 menters prove that the circulating fluid in healthy 

 animals is free from all bacterial organisms. To 

 obtain a supply for experimental purposes it must 

 be drawn directly from the vessels into a sterilized 

 receptacle. This may be accomplished by means 

 of a glass tube drawn out at each end to form a 

 capillary tube, hermetically sealed at each extrem- 

 ity and thoroughly sterilized by heat. Such a 

 tube is to be filled by exposing a superficial vein 

 of sufficient size, and introducing one of the ca- 

 pillary extremities within the vessel through a 

 very small orifice made through its walls. The* 

 end of the tube is to be broken off within the 

 vessel, after which the outer end may also be 

 broken, to allow the contained air to escape as the 

 tube fills with blood. This will not be necessary, 

 however, if a partial vacuum has been formed by 



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