424 ELIOT R. CLARK AND ELEANOR LINTON CLARK 



substance to be tested was injected subcutaneously into the 

 transparent fin expansion of the tail. The injections were per- 

 formed under the high power of the binocular microscope, with 

 glass canulae measuring about 20 micra at the tip. Before in- 

 jection, the fat was heated in a water bath to a temperature of 

 70°C., but was not boiled in order to avoid an alteration in its 

 chemical constitution. The olive oil and oleic acid were intro- 

 duced in the form of single globules, measuring about 50 micra in 

 diameter. The cream and yolk of egg, both of which consist 

 mainly of an emulsion of very fine droplets, were injected in the 

 form of a small irregularly shaped mass of approximately the 

 same size as the globules of oil. The various substances were 

 injected in different locations in different larvae; in some cases, 

 they were introduced near the edge of the fin at a distance from 

 lymphatics and blood capillaries, in others, they were injected 

 near the muscle edge and consequently nearer the vessels. 



The anaesthetized tadpoles were then observed, in chloretone 

 (1 to 5000) under the compound microscope, in a micro-aqua- 

 rium, by a method previously described (4). The cells and 

 vessels in the neighborhood of the injection were drawn, and 

 records made of them from day to day. 



Description of experiments 



The results of injecting each of the substances used will now 

 be described: 



1. Olive oil. As previously stated, the substance was injected 

 into the subcutaneous tissue of the tail, under the binocular 

 microscope and with the aid of fine glass canulae. The anaes- 

 thetized tadpole was then transferred to the micro-aquarium 

 and the oil and neighboring mesenchyme cells, blood-vessels 

 and lymphatics were drawn with the aid of the Leitz drawing 

 eye-piece No. 164. Immediately after injection, the oil globules 

 measured from 30 to 70 micra in diameter and were, as a rule, 

 oval in shape. From ten to twelve hours later they became 

 spherical. On one or two occasions in which the site of injection 

 became infected, the olive oil was extruded from the tail. In 



