1904.] The Chemical Regulation of the Secretory Process. 311 



environment, which is found in all living organisms from the lowest 

 to the highest. This adaptation may be conditioned by changes in the 

 food, or may arise as a reaction to the presence of harmful substances 

 in the surrounding medium. As an example may be mentioned the 

 mould Penicillium glaucum, which, as shown by Duclaux,'* when 

 grown on calcium lactate forms invertase only; on starch, however, 

 it produces amylase in addition, while on milk it produces a proteolytic 

 ferment and rennet. In the higher animals we have all the complex 

 processes by which an animal reacts to the introduction of living or 

 dead poisons, and which result in the production of an acquired 

 immunity. As part of the same process, if we accept Ehrlich's views, 

 we must include the process of assimilation of food, and the adaptation 

 of an animal to profound changes in its diet. 



But in all the higher animals the reaction of any part of the body 

 to external changes involves alterations in its relations to other parts, 

 and there is evolved a complex system of internal correlation of 

 the activities of organs, effected partly by the action of the central 

 nervous system, and therefore determinant of changes in form, partly 

 through means of the internal medium — the blood or similar fluid. 

 This latter mechanism of internal correlation has only recently entered 

 the domain of exact investigation. Thus the profound influence 

 exercised by the thyroid gland on the nutrition of the whole body, 

 specially of the central nervous system, and the production of a 

 substance by the suprarenal bodies which maintains the tone of all 

 contractile tissues in the body, have been disclosed to us during the 

 last 15 years. When chemical adaptation occurs in response to 

 changes either in the environment or in definite organs of the body, 

 the adaptive reaction may affect all cells of the body, or may be specific 

 in the case of certain cells. Only in the latter case will the results be 

 apparent to the morphologist as determinant of form. 



The researches which we wish to bring briefly before the Eoyal 

 Society have reference entirely to the last two groups we have 

 mentioned, and deal with the mechanism of adaptation to changes 

 in the food and the chemical correlation of the activities of different 

 organs engaged in the digestion and assimilation of the food. 



As we proceed down the alimentary tract, we find that each cavity 

 has its own set of reactive mechanisms arranged so as to pour on 

 the ingested food a juice which shall dissolve one or more of the 

 constituents of the food. In the mouth, as has been shown by 

 the researches of Ludwig, Heidenhain, Langley, and Pawlow, the 

 mechanism for the secretion of saliva is entirely nervous. The mucous 

 membrane is endowed with distinct sensibilities for different classes of 

 food, and the activity of the salivary glands is excited reflexly 

 according to the nature of the substance present in the mouth. In 



* ' Microbiologic,' toI. 2, p. 86. 



z 2 



