288 'PRINCIPLES OF GENERAL PHYSIOLOGY 



the culture medium, must have been utilised for the purpose. In the adult 

 animal the serum proteins are not used as food-stuffs. We have seen that 

 injection of such proteins does not increase the nitrogen output, although that of 

 amino-acids does (Quagliariello, 1912). On the other hand, tissue protein can be 

 used in starvation, so that we must admit the presence of enzymes in the cells able 

 to hydrolyse the proteins. It may well be that, in the growth experiments referred 

 to, these enzymes are called upon to hydrolyse the proteins of the plasma culture 

 medium before they are made use of by the growing tissue. 



The presence of autolytic enzymes in tissues can readily be shown by the use of 

 Alxlerhalden's "silk peptone," a polypeptide containing a large percentage of tyros inc. If a 

 small piece of tissue, say kidney, be immersed in a solution of this substance and kept at 

 40 the tissue will be covered in a few hours with crystals of tyrosine, from hydmlvsi* 

 of the polypeptide. 



A question cognate to this is the growth of tissue transplanted from one 

 part to another, investigated chiefly by Carrel (1910, 1912), Guthrie, and their 

 co-workers. This has been effected with blood vessels which were removed from 

 the body of the same animal some time previously. But it has been found 

 extremely difficult to transplant the tissues of one animal into another animal, 

 even of the same species. The transplanted tissue usually disappears sooner or 

 later, although, if previously killed by formaldehyde, it seems capable of serving 

 as a support for growth of new tissue on the part of the host. 



This fact argues an extraordinary complexity of some kind or other on 

 the part of the tissue protoplasm. The thyroid of one animal, for example, 

 is distinguished by another animal of the same species from its own thyroid. 

 Marshall and Jolly (1907), however, report success in two cases of transplantation 

 of ovaries from one rat to another, apparently remaining functional. Guthrie 

 (1908) also obtained fertile eggs from fowls whose ovaries had been replaced by 

 those of other fowls. Carrel and Guthrie (1906) report a case in which they 

 transplanted the kidneys of a dog into a bitch by vascular anastomosis and then 

 removed the kidneys of the bitch. The transplanted kidneys continued to secrete 

 normally for at least eight days, that is, up to the time at which the paper \\.IN 

 written. The urine contained no abnormal constituent with the exception of 

 a trace of protein. 



Further facts bearing on the question will be found in Chapter XXIV. 



INFLUENCE OF THE NERVOUS SYSTEM ON NUTRITION 



At an early period in the history of physiology it was supposed that the 

 only kind of efferent nerves were those causing contraction of muscles. After 

 the existence of nerves producing activity of the cells of secreting glands had 

 been proved by Ludwig and that of nerves causing stoppage of the heart by 

 the Webers, it was thought that there were nerve fibres presiding over growth 

 and repair. After section of certain nerves, which, in point of fact, always 

 contained sensory fibres, it was found that the skin, or other sensory surface 

 supplied by them, became inflamed and that wounds on such denervated surfaces 

 did not heal properly. Careful protection of these areas showed that there 

 was no real difference between them and normal areas. The absence of warning 

 on the part of the sensory nerves allowed the infliction of injuries, which 

 would otherwise have been avoided. 



Clara Jacobson (1910) made careful experiments on pigeons and on dogs and found that 

 there was no difference whatever between the rate of healing of wounds in normal and in 

 denervated areas. 



It is well known that organs grow in proportion to their use, but this is adequately 

 accounted for by the increased blood supply always associated with the activity of any tissue. 

 The manner in which this is ensured will be discussed in Chapter XXIII. 



After injury to certain parts of the central nervous system, in fever and 

 after the administration of certain chemical substances, there is a rise of 

 body temperature. Although this effect may be partly accounted for by 

 diminished loss of heat, owing to constriction of the blood vessels of the skin, 

 there appears to be evidence that, in some cases at all events, there is also 



