REACTION OF EMBRYONIC CELLS TO SOLIDS 525 



from the chick were incubated at about 39°C. The unusual 

 hot weather which lasted during almost the whole period when 

 the experiments with chick tissues were under way rendered 

 unnecessary any precautions to keep the tissues warm during 

 their preparation and examination. 



The preparation of the spider web for the experiments was the 

 only innovation in technique that needs special description. 

 It was necessary to have the wel3 tensely spread over a suitable 

 frame so that it would support the drop of fluid from below. 

 For this purpose glass rings were employed, since they were easy 

 to sterilize and well adapted to form the wall of a moist chamber. 

 A number of rings were placed in clean glass aquarium jars and a 

 single spider introduced, which in the course of a day or two 

 spun a web covering the whole bottom of the jar. The rings were 

 then lifted out with forceps and the web cut or torn off around 

 them. The slight roughness of the rim of the glass was sufficient 

 to hold the web tense. The rings with the web upon them were 

 sterilized by dry heat, the web standing a temperature of 150°C. 

 without injury. In making the spider web preparations, the 

 rings were first fastened to the slide with vaseline. A small 

 di'op of the culture fluid was then placed upon the web and the 

 tissue afterwards introduced by means of a capillary pipette. 

 It was unfortunately necessary to use very small drops of fluid 

 since the weight of large drops caused the web to sag and touch 

 the bottom of the chamber. The small size of the drops is 

 sufflcient to account for the relatively unfavorable results ob- 

 tained by this method, the tissues usually not growing with very 

 great luxuriance. After mounting the tissue upon the web, a 

 cover-slip was placed over it and sealed on by vaseline. The 

 weight of the cover-shp flattened out the small drop and the 

 tissue was thus in contact both with the cover and the, web. 

 In most cases the covers themselves were coated with web so 

 that the tissue was kept between two layers of this material. 

 During the early part of the season there was some difficulty 

 in finding a sufficient number of suitable spiders for the purpose.'^ 



i« I am greatly indebted to Prof. A. Petriinkevitch for advice and assistance 

 in collecting this material. 



