G. GENERAL NATURAL HISTORY AND ZOOLOGY. 327 



tioii of red or violet, was of normal length. He finds that 

 all those pathologically color blind sufter from atrophy of the 

 optic nerve by reason of cerebral or spinal injuries, the atro- 

 phy being of a peculiar nature, such that the fibrous and cel- 

 lular layers of the retina and the optic nerve to the brain were 

 atrophied, but not the so-called rods and cones. In retinal 

 diseases, on the other hand, the perception of colors is not 

 perverted, though diminished. Dor therefore concludes that 

 color blindness is a cerebral afiection. 12 A, 1873, 375. 



THE INJURIOUS INFLUENCE OF COMPRESSED AIR ON THE HU- 

 MAN ORGANISM. 



It is well known that in many engineering enterprises it 

 is necessary for men to work beneath the earth in an atmos- 

 phere of compressed air, whose influence upon the health and 

 life has frequently been considered as highly injurious; while 

 by others it has been maintained that the influence is not 

 necessarily injurious. A series of exact experiments on this 

 subject has been made by a number of French and German 

 2)hysicists, whose conclusions may be summed up as follows: 

 All observers of the influence of compressed air agree that 

 the sufierings connected therewith depend less upon an in- 

 creased pressure than upon a sudden return from a com- 

 pressed atmosphere into the normal air, whereby the blood 

 that has been strongly compressed in the membranes of the 

 body is too rapidly driven to the lungs and the heart, and 

 causes injurious hemorrhages. It is important now to de- 

 termine what rules shall be adopted whereby accidents from 

 this source may be lessened. 



First. The laborers in compressed air should be only sound 

 and strong persons, having especially strong lungs. 



Second. The compression of the air in the working-cham- 

 ber should be gradual, so that the maximum compression is 

 reached fifteen minutes after the workman enters the chamber. 



Third. The compression of the air should not exceed three 

 atmospheres. 



Fourth. The time durino: which the workmen continue in 

 the chamber should not exceed four hours. 



Fifth. The men should be provided with water-proof boots 

 and woolen stockings, to protect their feet from the cold and 

 the wet. 



