VISION 503 



Red. This test is applied to those completely 

 color-blind. Continue the test until the person 

 examined has placed beside the specimen all the 

 skeins belonging to this shade, or else, separately, 

 one or more " colors of confusion." 



The red-blind chooses (besides the red, green, 

 and brown) shades which to the normal sense 

 seem darker than red. The green-blind selects 

 opposite shades, which seem lighter than red. 



Violet Blindness. Very rare. Recognized by 

 a confusion of purple, red, and orange, in the 

 purple test (see 2). Much care is required to 

 diagnosticate this form. 



The Respiration Scheme. 1 The glass cylinder 

 (Fig. 67) represents the thorax. The surface of the 

 water in the glass cylinder represents the diaphragm 

 and movable chest walls ; its level may be changed 

 by raising or lowering the large rubber tube, in the 

 free end of which is placed a second glass cylinder, 

 not shown in Fig. 67. The interior of the cylinder 

 above the water represents the thoracic cavity, and 

 the rubber balloon the lungs. The paraffined cork 

 is pierced by a pleural and a tracheal tube. The 

 upper end of the pleural tube enters a rubber tube, 

 in the wall of which is a small hole closed by a short 

 glass rod. Through this hole the pleural cavity may 

 be opened to the atmospheric air. The tracheal tube 



1 American Journal of Physiology, 1904, x, p. xlii. 



