RELATIONS OF THE ORGANS TO ONE ANOTHER. 615 



tissue requires oxygen for the performance of its functions. This may be 

 shown very prettily by means of methylene blue. As we have seen, this 

 dyestuff is deprived of oxygen by the tissues, and is thereby transformed 

 into the colorless reduction product. If the colorless organ is subse- 

 quently exposed to the air for some time, gradually the blue color of 

 methylene blue reappears. In the case of narcotized animals in which 

 the brain has been made inactive, the brain substance remains blue, so 

 that evidently under these conditions the tissue does not require oxygen. 1 

 The abundance with which the nerve-centers are supplied with blood- 

 vessels is an indication of their high oxygen requirement, and in fact 

 anaemia in these places causes severe disturbances, eventually leading 

 to the loss of function. 



It might be thought that some idea concerning the metabolism of nervous 

 tissue might be gained by seeking the end-products. As a matter of fact, 

 in the cerebro-spinal fluid, which in a sense may be regarded as the lymph 

 of the brain, choline, a decomposition product of lecithin, has been found. 

 This, however, does not give us much information. We do not know 

 whether choline is to be regarded as a true metabolic end-product, or 

 whether it is not more probably produced by the destruction of nerve- 

 tissue, and is far from being concerned in true metabolism. Its detection 

 has usually been an indirect one and not quantitative. The fact that an 

 increased amount of choline appears in degenerative processes indicates 

 that its formation corresponds to a destruction of nervous tissue, so that 

 it is not to be considered as a normal metabolic product. We do not wish 

 to place any great weight upon this discovery of the presence of choline, 

 and would rather take the attitude that at present we know nothing what- 

 ever concerning the metabolism in nervous tissue. It is also hardly to be 

 expected that there will be much progress in this direction for a long time. 

 There is no foundation for research. Even our knowledge of the compo- 

 sition of nervous tissue is extremely faulty. We have only to remember 

 that, with few exceptions, we know but little concerning the metabolism 

 of those cells of the body which are much more readily accessible. We 

 recognize only the total results of metabolism, and are, as a rule, ignorant 

 as regards the part taken by the separate organs. We shall soon come 

 back to the fact that it is impossible to detect any effect of intense mental 

 effort in metabolism experiments. 



We might perhaps expect that pathology would tell us something 

 concerning the metabolism in nervous tissue. We know that there exist the 

 so-called functional nervous diseases, i.e., diseases which, according to the 

 general assumption, are not caused by any anatomical change of the 



1 C. A. Herter and A. N. Richards: Am. J. Physiol. 12, 207 (1904). Cf. H. von 

 Bayer: Z. allg. Physiol. 2, 169 (1902). Frohlich: ibid. 3, 131 (1903). Frohlich and Tait: 

 ibid. 4, 105 (1904). K. H. Baas: Pfliiger's Arch. 103, 276 (1904). 



