44 THE STRUCTURE OF THE GLANDS OF BBUNNEB 



mammals, and indeed of different tubules of the same animal, stain with different 

 degrees of facility. They conclude that the depth of staining indicates the amount of 

 mucin present in the cell, and that some cells contained a great deal of inucin, others a 

 little, and still others none at all. The uniformly intense stain obtained by the writer 

 by means of his muchsematein technique shows that this conclusion is not justified. 

 The cells are to all appearance in all mammals equally engaged in inucin secretion. 



Does the different capacity for staining in these synthetic dyes indicate, as 

 Schaffer (1891) thought, a difference in the nature of the mucins formed? It is, of 

 course, possible that this is the case. We already know many different mucins, nnd 

 we have reason to suspect, as Huppert (189G) has suggested, that there is a great 

 number of different glycoproteids. Although it is possible that different mucins are 

 secreted by the glands of Brunner in different mammals, it does not appear to me to 

 be necessary to assume that this is the case in order to explain the different staining 

 properties. 



It is known that the mucous cells do not store their secretion as mucin, but as a 

 substance (mucigen) which may readily be transformed into mucin. It is not possible 

 definitely to identify the granules visible in the cell as mucigen, but they are probably 

 composed of one of the antecedents of mucin, and not of mucin itself. It is, more- 

 over, probable that the transformation of the substances received by the cell into niuciu 

 is not accomplished by one or even two steps, but that there are many stages in this 

 chemical process. Furthermore, it is a well-known fact that similar cells from differ- 

 ent sources, engaged in the formation of the same product, may store it in the form of 

 different antecedent substances. For example, the chief cells of the glands of the 

 gastric fundus of the rabbit in the resting condition are filled with zymogen granules 

 and contain little prozymogen. The similar cells of the glands along the greater cur- 

 vature contain few granules, but a great deal of prozymogen. These cells differ, as 

 Langley (1882) pointed out, in secretory equilibrium. 



It is conceivable that mucous cells similarly differ in secretory equilibrium, and 

 that, while the ultimate product of their secretory activity may be the same substance, 

 they contain the antecedent substances in varying proportions. Some such explana- 

 tion as this must be resorted to, in order to explain why similar cells of the same tubule 

 differ in their staining capacity. 



The glands of Brunner of the rabbit are mixed glands. The bulk of the cells 

 composing the tubules are mucous cells similar in all important respects to those in 

 other mammals. In many cases the dark cells forming the terminal acini or tubules are 

 specifically different from the mucous cells. There are no intermediate stages, and 

 these cells do not under any conditions contain mucin or its stainable antecedents. 

 They contain zymogen granules, easily visible (as Schwalbe first pointed out) in the 

 fresh cell, and prozympgen. By the microchemical reactions for iron and phosphorus 

 these elements may be demonstrated to be fundamentally different from the contents 

 of the mucous cells. 



320 



