Sli 



The covorf^lassos nrc laid on the tabic and a drop of 

 l)lasnia delivered Iroin llie pipelle which has to be kept 

 slrielly vi'i-lical in older (o (h'liver even-sized drops. The 

 pipettes are cnlihiMled so Dial Ihev all deliver dro|)s ol" prac- 

 tically tlie same size. The plasma is spread out with the 

 cataract knil'e so that it covers an area ol' about 10- 15 m. ni. 

 in diameter. With the point ol' llie knil'e Ihe little I'rag- 

 ment of tissue to be cultivated is placed in the i)lasma and 

 a drop of the embryonic tissue juice is added and the mix- 

 ture stirred with the knil'e. Small amounts of vaseline arc 

 placed on the hollow slides and they are inverted and pla- 

 ced over the coverf^lass lying on the table. This has to be 

 done rather (piickly to avoid loo much evaporation from 

 the culture media. After a minute or so the coagulation of 

 the cullurt medium has taken place and the slides with 

 the cover glass can be taken up and sealed with paraffin. 

 Immediately after the preparation they are placed in the 

 incubator (39° C). Here they are allowed to grow undis- 

 turbed for 18 lioui's, after which time they are transferred 

 to a fresh nu'dium. The coverglass is lifted with the heated 

 point of a blunt cataract knife. It is then placed upon a 

 piece of black glass or similar material of about one inch 

 thick. It is necessary for cutting the cultui'e to be able 

 to lowei' the wrist sufficiently to place the cutting edge of 

 the knife i)arallel willi Ihe surface of the culture. The tiny 

 tissue-fragnu'ut and its crown of new growth can be seen 

 better on the black background. The fragment is extirpated 

 bj' four clean cuts made with the blade of a sharp cataract 

 knife within the area of new growth and divided into two 

 or three pieces of as equal a size as possible. The pieces 

 are transferred with the point of the knife to an oval slide 

 containing Ringer's solution. They are allowed to remain 

 in the bath for about i^^ seconds.- In the meantime the new 

 medium is jjrepared on the coverglasses in the way just 

 described and the fragments placed in il. ^^ hen many cul- 

 tures have to be changed, it is safest to take a new knife 



