198 G. E. COGHILL 



acid than there was in the acid. According to the records of the 

 experiment, there were five movements among forty embryos 

 during the minute in the pond water originally, indicating the 

 degree of normal activity. In the HCl n/1000 there were 60 

 movements during the same period, while there were 151 move- 

 ments during the one minute of immersion in pond water after the 

 bath in HCl n/1000. These data certainly prove that, while 

 the acid excited response, it rendered the skin abnormal in some 

 respect. 



With view to determining the nature of the action of very dilute 

 solutions of hydrochloric acid upon the skin of these embryos, 

 specimens were selected which had not nearly reached the stage 

 of earliest response and which exhibited the typical ciliary move- 

 ment over the surface of the skin. In these embryos the reaction 

 of the skin alone was studied without the intervention of nervous 

 or muscular phenomena. 



Embryos of this age, when immersed in pure water in which fine 

 granulated carmine is suspended, keep the surface of the body clear 

 of this substance indefinitely. In such a preparation the carmine 

 particles may be seen under the microscope in a perpetual stream 

 over the surface flowing cephalo-caudad and off at the caudad end 

 of the animal. If, however, the embryo is immersed in HCl 

 n/1000 in which finely pulverized carmine is suspended, the par- 

 ticles begin to adhere to the surface of the skin in less than two 

 minutes. The cilia beat vigorously among the accumulating 

 carmine particles but fail to dislodge them so long as the embryo 

 remains in acid. Immersion in a stronger solution of the acid 

 produces this effect more quickly and in a short time causes the 

 exudation of globules of adhesive substance on the surface of 

 the ectodermal cells. Prolonged immersion intensifies this action 

 till the complete disruption of the cells occurs. And when this 

 disruption occurs it is most pronounced in the regions where the 

 particles of carmine first adhere in the dilute acid solution. Par- 

 ker ('12) places the threshold of stimulation by hydrochloric 

 acid in the mouth of man at n/1000. This being correct, the ecto- 

 dermal cell of the amphibian embryo which has no nerve supply 

 responds directly to as great a dilution of the acid as does the 



