TISSUE-CULTURE IN VITRO lOJ 



centrifuged and decanted is the 'embryo juice'. No one so far 

 has ever been able to replace it by any synthetic medium. 

 This product is now also employed medically to avert surgical 

 shocks. 



Needless to say, these operations must all be accomplished 

 with infinite aseptic precautions, far greater than for a surgical 

 operation. The preparation of the saline solutions {Tyrode 

 and Ringer solutions) also demands great care. The sub- 

 stances employed must be rigorously pure and the degree of 

 alkalinity (measured by the concentration in hydrogen ions 

 expressed by the symbol pH) is controlled electrically or 

 colorimetrically. In addition to the 'juice' there is also the 

 'support' which is composed of a drop of coagulated chicken 

 plasma. (We remind the reader that the blood is composed of 

 red and white blood-cells suspended in a liquid called the 

 plasma^ which coagulates under different influences.) The 

 culture, one or two square millimetres in size, is placed in this 

 drop or on its surface, according to the nature of the cells to 

 be cultivated. The blood is taken from a young and healthy 

 chicken by means of a sterile operation made under anaes- 

 thesia. The blood-cells are separated from the plasma by 

 centrifugation in tubes previously paraffined and cooled at 

 0° C. so as to prevent coagulation. 



When these elements have been prepared, all that remains 

 to be done is to take an incubated egg, about nine or ten days 

 old, remove the embryo, dissect the heart, or any other part 

 of the animal, cut out a certain number of small pieces without 

 tearing them and incorporate them on a thin sUde into a drop 

 of plasma mixed with a drop of embryo juice. The mica is 

 then covered by a thick glass slide hollowed out in the middle, 

 sealed with hot paraffin, and put into an incubator at 38° C. 

 Forty-eight hours later, the fragments are extracted and cut 

 with a cataract knife, the blade of which is only three milli- 

 metres long. They are then washed in Tyrode solution and 

 quickly replanted into a new nutritive drop before the latter 

 has had time to coagulate. This is done every two or three 

 days according to the nature of the tissue. The small pieces 



