350 PRINCIPLES OF GENERAL PHYSIOLOGY 



in the fact that addition of saliva to the perfusion fluid causes the gland to secrete. 

 The exciting substance is apparently of a compound nature, since, after heating to 

 65 C., saliva has lost its power of producing secretory activity from rest although 

 it is still capable of accelerating the rate of flow when this has nearly stopped, 

 subsequent to stimulation of the chorda tympaiii nerve. 



The work of Hustin (1912, 1913) on the pancreas is also of interest in this 

 connection. Perfusion with oxygenated Ringer's solution, to which secretin has 

 been added, does not result in secretion ; the addition of the blood or certain 

 liquids derived from it, such as hydrocele fluid or lymph, is also necessary. The 

 author concludes that secretin, oxygen, electrolytes, and some substance contained 

 in blood must be simultaneously present. As far as oxygen is concerned, the 

 experiments are conclusive. A mixture of blood, secretin, and saline solution, 

 effective when oxygenated, becomes ineffective when the gases are pumped off. 

 We can readily understand the necessity of electrolytes for maintaining the 

 normal character of the cell processes, and Hustin's experiments show that blood 

 dialysed against isotonic sodium chloride solution is much less effective than 

 normal blood ; even dialysis against Ringer's solution seems to deprive it of some 

 important diffusible constituents, since it is not as effective as non-dialysed blood, 

 although greatly superior to that deprived of all its diffusible constituents except 

 sodium chloride. 



For example (1913, p. 89), the amount of juice obtained in sixteen minutes by the use of 

 the latter was 0'05 c.c. ; if dialysed against Ringer's solution, 0'33 c.c. in fourteen minutes, 

 rather more than seven times as much ; with normal blood, 0'70 c.c. in fourteen minutes, or 

 twice as much as the preceding. 



The necessity of the presence of some substance contained in blood, other than 

 haemoglobin, as carrier of oxygen, is not so satisfactorily shown. Washed red 

 corpuscles were found to answer the purpose of the whole blood ; although one 

 experiment was performed with a solution of haemoglobin, which was found 

 ineffective, it must be noted that the material used was a dried preparation by 

 Merck, which probably consisted of methaemoglobin and could not, if so, act as 

 an oxygen carrier. The evidence that certain tissue extracts and lymphatic 

 fluids do not owe their favouring property to their being better oxygen carriers 

 than the saline solution is not sufficient. Moreover, it was found impossible to 

 separate any constituent from these liquids which was able to take the place of 

 blood. The explanation of the process, on the lines of the Bordet-Ehrlich theory 

 of haemolysis, does not throw much light on its actual nature. 



ELECTRICAL CHANGES 



A fairly considerable amount of work has been done in connection with the 

 difference of potential found, on stimulation, to occur between that end of a 

 gland cell which is in relation with the duct, or free surface, and that end in 

 relation to the blood supply. The cause of this phenomenon has not yet been 

 made out, but there are one or two points in the process which have a bearing 

 on the questions before us. 



Although it had been known for many years that the various glandular 

 tissues of cold-blooded animals, and also the sweat glands of the mammal, gave 

 rise to electrical changes on excitation, it was not until 1885 that it was possible 

 to investigate the different effects in the salivary glands produced by different 

 nerves from this point of view. In that year, in conjunction with Bradford, I 

 was able to show that the potential difference between the hilus of the gland 

 and the opposite surface, that is, between the duct and the surface of the cells 

 turned towards the blood vessels, is of the opposite sign when the chorda tympani 

 nerve of the dog is excited to that when the sympathetic nerve is excited. If 

 the curves of Fig. 93 are consulted, it will be seen that the former is accompanied 

 by a large secretion of saliva, which follows a course very nearly parallel to the 

 electrical change, whereas the latter, of the opposite sign and much smaller, 

 results only in the formation of one drop of saliva. The support which these 

 two opposite effects give to the hypothesis of two different kinds of nerve fibres 



