MUSCLE TONUS AND CO2 OUTPUT 49 



BLACKENING BOTH EYES 



When one eye or parts of one or both eyes of an animal are 

 blackened, the characteristic changes in posture, etc., are pro- 

 duced; but slight disturbances to the animal due to the partial 

 blackening cause it to try to remove the varnish with its front 

 legs. Such movements are not easily eliminated, and hence no 

 satisfactory results on the CO2 determinations are possible. 

 However, when both eyes are completely blackened, the animal 

 makes no attempt to remove the varnish, but remains motion- 

 less. 



Carbon-dioxide determinations on the animal before blacken- 

 ing its eyes are, with proper handling and manipulation, rather 

 easily and accurately made. In the experiments herein reported 

 at least two or three separate determinations, in which there were 

 no detectable body movements, were made and the average rate 

 of CO2 output for the normal animal then obtained. No dif- 

 ference in movements of the animal in the normal and eye-black- 

 ened condition could be detected, so results are not, to any ap- 

 preciable extent at least, modified by CO2 produced as the result 

 of body movements. 



Table 1, in which are listed results of some ten typical experi- 

 ments, show^s the time taken to produce the same amount of 

 CO2 by an animal when normal and with eyes blackened. In 

 ahnost every case a marked decrease in the rate of CO2 output is 

 noted. Those animals, in which the decrease in rate of CO2 out- 

 put was not so marked with eyes blackened, w^hen decapitated 

 also showed a comparatively small decrease in rate. These slight 

 decreases in rate of CO2 output in certain animals can doubtless 

 be attributed to the physiological condition of the particular 

 organism. 



Figure 1 show^s graphically the average decrease in rate of CO2 

 output for fifty individuals. 



To show that this decrease in rate of CO2 output was due to 

 the effects of blackening the eyes, and that after removal of the 

 varnish the animal assumed its normal conditions, the following 

 experiment is cited. Individuals were taken, the normal rates 

 of CO2 output determined, and then the eyes blackened. The 



