CHAPTER XXXVII. 553 



1040. Removal of Plasma. When dogs, rabbits, cats, chickens, 

 guinea pigs and rats are used, the carotid artery is ordinarily 

 selected ; an incision is made in the mid-line in the neck, and as 

 soon as the skin is divided the edges are clipped to sterile towels. 

 The carotid is exposed, its distal end ligatured and its proximal end 

 clamped. A little sterile oil is placed on the artery, which is opened, 

 and one of the cannule from the sterile oil is taken, inserted and tied 

 in position ; on releasing the clamp the blood flows freely. This is 

 collected in the paraffined test tubes for centrifuging. The tubes 

 should be in their ice- jackets ; they are corked at once and im- 

 mediately centrifuged for about five minutes ; they are then removed 

 and placed in an ice box at C. 



For human plasma one may remove blood from a vein by means 

 of a needle pipette sterilised in olive oil. 



After the centrifugilisation the supernatant plasma may be 

 removed with pipettes coated in paraffin ( 1039). It should be 

 used immediately for making the cultures, but can be preserved for 

 some time in a fluid condition if kept very cool. Chicken plasma 

 can be so preserved for more than a week, human and dog plasma 

 for a few days, while rat plasma always coagulates after a few hours 

 (CARREL and BURROWS, Journ. Exp. Med., 1911) ; when coagulation 

 takes place the plasma is no longer of use. 



CARREL and BURROWS (Jour. Exper. Med., xiii, 1911) found that 

 dilution of the plasma had a marked influence on the rate of growth of 

 splenic tissue ; normal plasma is not the optimum medium for growth 

 of tissue ; the most favourable plasma for spleen culture contains two- 

 fifths distilled water, and slightly less for liver and heart, and generally 

 for skin, too. 



1041. Preparation of Tissues. The tissues for cultures should be 

 in normal condition, and are best when taken from the living animal 

 or immediately after death. Positive results can still be obtained, 

 however, when the tissues have been deprived of circulation for 

 more than thirty minutes. 



With a cataract knife and a fine needle, a small fragment of tissue 

 is dissected from the animal and placed on a glass plate ; the piece 

 is rapidly cut into smaller pieces about the size of a millet seed and 

 transferred to a perfectly clean sterile coverslip. This process must 

 be carried out rapidly because some tissues die in even as short a 

 time as ten seconds when exposed to the air (e.g., thyroid). To 

 prevent this the tissue may be dissected in serum or Ringer. 



1042. Preparation of Cultures. For cultures of the hanging-drop 

 type one uses a hollow ground slide of a sufficient depth to prevent 



