378 THE POPULAR SCIENCE MONTHLY. 



pressed, irritable, melancholy, and, it may be, stupid and forgetful, 

 after a few months' work, although every part of his body may be 

 organically healthy, and a month's holiday may be sufficient to restore 

 every organ to perfect functional activity ? One reason, no doubt, 

 may be that his systematic overwork may produce a diminution in the 

 energy-yielding substance of his nerve-centers, just as we see that a 

 certain amount of atrophy occasionally occurs in overworked muscles. 

 But this does not seem very probable. It seems much more likely that 

 they cease to act in the normal way because, during each day's activ- 

 ity, a certain amount of waste product is formed which is not perfectly 

 removed during the hours of rest. 



All throughout the body we have most elaborate arrangements for 

 removing waste products. In the muscles, for example, we find that 

 the fascia which surrounds them forms a regular pumping arrange- 

 ment, the two layers of Avhich it consists being separated from each 

 other at each muscular relaxation, and pressed together at each con- 

 traction.* The lymph and the waste products which it contains are 

 thereby actually pumped out of the muscle at each contraction, and 

 sent onward into the larger lymph-channels, so that the muscular action 

 itself removes the waste products. At the same time we find that the 

 movement of the muscles of the leg, for example, will also pump out 

 the blood from the veins, sending it upward from the feet, and press- 

 ing it upward to the body.f 



Again, we find that in the abdomen and thorax we have pumping 

 arrangements, whereby any excess of the serous fluid which bathes the 

 intestines and lungs is pumped out of the peritoneal pleural cavities by 

 the action of respiration. The two layers of the central tendon of the 

 diaphragm and of the pleura here form pumping arrangements similar 

 to the fascia in the leg. 



The brain and spinal cord, being inclosed in rigid cases, have no 

 pumping arrangements in immediate connection with them, but the 

 circulation of the cerebro-spinal fluid in them is probably affected also 

 by the movements of the thorax and abdomen. The cavity of the 

 arachnoid and of the cerebral ventricles is not only continuous with 

 similar cavities in the spinal cord, but also with the lymph-space sur- 

 rounding the choroid, with the interior chamber of the eye, and even 

 with the lumbar lymphatics ; and Professor Schwalbe has succeeded 

 in injecting these parts by a single insertion of the nozzle of his inject- 

 ing syringe into the arachnoid. His observations have been confirmed 

 and extended by Althann.J The experiments of Quincke have shown 

 that during life a current exists in the cerebro-spinal fluid, both from 

 above downward and from below upward. The cause of this current 



* Ludwig and Gencrsich, p. 53, "Ludwig's Arbeiten," 1870. 



f Braune, "Ber. der siichs. Gesell. d. Wiss.," 1870, p. 251. 



X Althann, vide " Virchow's Jahresbericlit," 1872, p. 156. 



Several authors, as Abel Key and Retzius (" Nordisk medicinsk Arkiv.," 1870, 



