352 PRINCIPLES OF GENERAL PHYSIOLOGY 



is obvious. Just as the sympathetic fibres are known to require a larger dose 

 of atropine in order to paralyse them than the chorda fibres do, so the electrical 

 change from the latter nerve was abolished by a much smaller dose than that 

 from the sympathetic. But this refers only to that part of the electrical effect 

 from the chorda which is of opposite sign to that of the sympathetic. After a 

 dose of atropine sufficient to paralyse the "secretory" fibres of the chorda, 

 excitation of this nerve gave a small electrical effect of the same siyu as tli.it 

 from the sympathetic. This effect, normally, is swamped by the much larger 

 opposite one and is, no doubt, due to fibres of the same kind as those which 

 preponderate in the sympathetic. That vaso-motor effects are not concerned 

 in the phenomena is shown by the fact that the electrical changes tire abolished 

 by atropine, which does not affect the vascular ones. In the cat, as was shown 

 by Langley (1878), both nerves produce a watery secretion and, accordingly, 

 we find that the electrical change from both is of the same sign as that of the 

 chorda in the dog, but is usually followed by one of the opposite sign. 



We therefore drew the conclusion that the electrical change of the sign of 

 the typical chorda effect in the dog is due to the flow of water (together with 

 salts of the blood) and that the other one is connected with the elaboration 

 of the specific organic constituents of the saliva. 



Further evidence of the same kind was given by the later experiments of 

 Bradford (1887). Two experiments are of particular interest (pp. 92, 93). The 

 sympathetic in the dog was being excited, giving the usual scanty viscid secretion, 

 with the usual small electrical change. Suddenly a large electrical change of the 

 opposite sign appeared and, coincidently, a copious secretion of watery saliva. In 

 the second experiment the chorda had been stimulated at intervals for an hour 

 and a half. After such treatment, as Langley showed (1889), and as would not 

 be unexpected, since both nerves act on the same cells, stimulation of the 

 sympathetic is apt to give a watery secretion for a time. This was the case in 

 Bradford's experiment, but the watery secretion appeared only after a long 

 latent period, during which the electrical effect was of the usual " sympathetic " 

 sign. As soon as the watery secretion appeared, there was a change in the 

 sign of the electrical effect. After a period of rest, the sympathetic failed to give 

 the watery secretion and the usual " sympathetic " electrical effect reappeared. 



The possible causes of these changes will be best appreciated after Chapter XXII. has 

 been read. That the chorda effect is not due to mere flow of liquid along the ducts is shown 

 by another experiment of Bradford's (p. 98) in which clamping of the duct had no effect on 

 the electrical change. Removal of the clamp, after stimulation had been stopped, produced 

 no electrical etfect, although a free flow of saliva took place along the ducts. The electrical 

 change is therefore due to phenomena in the cells themselves. 



The corresponding changes in the sweat glands (Hermann and Luchsinger, 1878, 1), in 

 the frog's skin (Hermann, 1878) and tongue (Hermann and Luchsinger, 1878, 2) may be 

 mentioned, since they are easily observed. 



PRODUCTION OF LYMPH 



This phenomenon, as due to increased osmotic pressure in the fluid of the lymph 

 spaces, on account of the diffusion into them of the small molecules of the 

 products of metabolism of the active organ, has been described above (page 165). 



The detailed observations of Bainbridge (1900) on the submaxillary gland 

 should be consulted. 



ADAPTATION 



The possibility of increased production of an appropriate enzyme, in response to 

 the stimulus of a particular article of food, has occurred to several investigators 

 and positive results are said to have been obtained. 



Careful testing by subsequent observers, however, showed the presence of 

 unsuspected sources of error. The only case in which any satisfactory evidence 

 exists is that of the increased amyloclastic action of the saliva, as described by 

 Lovatt Evans (1913, 1). Carbohydrate food only had this effect and mere 

 chewing, without swallowing, is ineffective. The simplest explanation is that r 



