282 S. J. HOLMES 



extent unless they are in a medium of more or less firm consist- 

 ency. When the lymph does not form a coagulation about the 

 tissue no outgrowth occurs, although the cells may remain 

 alive and the cilia upon them keep beating for weeks. In 

 Ringer's solution epithelium from both embryos and adults will 

 remain alive for a long time, but no outgrowth as a rule takes 

 place. As so many cultures put up in frog's lymph proved un- 

 successful the attempt was made to find a substitute for coagu- 

 lum of blood and lymph which would elicit the same sort of 

 thigmotactic reaction from the epithelial cells. After several 

 experiments which proved to be failures, it was found that a 

 mixture of Griibler's nutrient gelatin and blood serum afforded 

 a culture medium that was very suitable for the purpose in hand. 

 The proportions of the substances finally decided upon were 

 about equal parts of serum and a two per cent solution of the 

 gelatin. The gelatin solution was made and sterilized by boil- 

 ing. In obtaining the serum, blood was drawn from the heart 

 into a small glass tube and the clot removed. Then the gelatin 

 warmed sufficiently to become fluid was mixed with an equal 

 quantity of serum and centrifuged to remove the blood cor- 

 puscles, and the clear liquid was then transferred to another 

 receptacle. The mixture thus formed becomes quite fluid when 

 but slightly warmed and remains fluid for an hour or more at 

 ordinary temperatm'es. One can work with it therefore with- 

 out undue haste, and should the supply become solidified in the 

 course of making preparations of the tissues it can be made 

 fluid again by a slight degree of warmth. The same fluid may 

 be preserved for several days if kept free from infection. I have 

 found tissue to thrive in it after it had been prepared for several 

 days as well as in mixtures freshly made. The ease with which 

 this medium can be made and used greatly facilitates making 

 preparation of tissues, and the results obtained by its use are 

 also more uniform than those obtained by the use of plasma or 

 IjTiiph. 



The ectoderm from pieces of young tadpoles grows out in this 

 medium with great rapidity. In twenty-four hours the new 

 growth may exceed the area of the introduced tissue and in 



