1218 PHYSIOLOGY 



system. Leaving the cord by the white rami communicantes from the 

 second dorsal to the third or fourth lumbar nerves, they pass into the 

 sympathetic chain. Here the first relay of fibres ends in connection with the 

 cells of the sympathetic ganglia, and a fresh relay of fibres, which are non- 

 medullated, pass from the cells along the grey rami into the various spinal 

 nerves, to be distributed to the whole surface of the skin. The secretion of 

 sweat by the sweat glands may be roused by the injection of pilocarpine even 

 after division of the sweat nerves, so that this drug must act peripherally 

 on the glands. The action of pilocarpine, as well as the effects of artificial 

 stimulation of the sweat nerves, is abolished by the administration of 

 atropine. 



THE GASEOUS EXCHANGES OF THE SKIN. In any animal with a 

 thin moist skin, such as the frog, the absorption of oxygen and the excretion 

 of C0 2 from the skin may be sufficient for the proper aeration of its blood, 

 so that it may continue to live after the extirpation of its lungs. In man 

 there is also a continuous output of C0 2 through the skin, but the amount 

 leaving the body in this way is negligible compared with that which is 

 exhaled tnrough the lungs. The loss of C0 2 by the skin rises with increase 

 of external temperature. Thus at a temperature of 29 to 33 C. the C0 2 

 output by the skin is about 0-35 grm. per hour, i. e. about 84 grm. in the 

 twenty-four hours. When the external temperature rises above 33 C., 

 the C0 2 output increases, so that at 34 it is doubled and at 38-5 it may 

 amount to as much as 1-2 grm. per hour (Schierbeck). It is just at this 

 temperature of 33 C. that a secretion of sweat begins to be noticeable, so it 

 has been suggested that the increased C0 2 output may be due directly to the 

 increased work and metabolism of the sweat glands during their activity. 



ABSORPTION BY THE SKIN. In order to test the alleged influence of 

 baths containing medicinal substances in solution, many experiments have 

 been made to determine whether absorption is possible by the skin. It 

 may be regarded as established that the uninjured skin is impermeable 

 for watery solutions of salts or other substances. On the other hand, it is 

 possible to produce a certain amount of absorption by the inunction of 

 substances dissolved in fatty vehicles. Thus the administration of mercury 

 is often carried out by the inunction of mercurial ointments, and the fact that 

 mercurial salivation may be produced in these conditions shows that a certain 

 amount of the mercury must have been absorbed. It is difficult to imagine 

 that any appreciable amount of cod liver oil will be available for the nutrition 

 of the infant when this substance is administered by rubbing it on the skin. 

 On the other hand, the moist mucous surfaces, such as the conjunctiva or 

 the mucous membrane of the respiratory passages, as well as raw surfaces of 

 the skin, e.g. which have been deprived of their epidermal layer by the 

 application of blisters, permit of the rapid passage of substances in watery 

 or oily solution. 



