HYPOPHYSEAL MORPHOLOGY 



173 



Reactivity in this sense, by enabling the 

 significance of tinctorial or morphologic 

 differences to be tested, is of primary im- 

 portance both in the verification of parti- 

 tions based on tinctorial or morphologic dif- 

 ferences and in the identification of cell 

 types as secretors of specific hormones. Only 

 those differences which are correlated with 

 a difference in reactivity, and which can be 

 related to the production of specific hor- 

 mones, can be regarded as of specific signifi- 

 cance. Variations in the size and shape of 

 the cell or its nucleus, the amount of cyto- 

 plasmic basophilia, the form of the Golgi 

 apparatus, and the amount of granulation 

 may be related to variations in the state of 

 activity in the single cell type and are, 

 therefore, of functional significance but not 

 of specific value. 



D. SPECIFICITY OF GRANULES 



One implication of the method of classi- 

 fication formulated here is that all the se- 

 cretory granules within any one cell will be 

 of a single type. This seems to be true of 

 the majority of mammals, judging from my 

 own observations. Admittedly it is possible 

 with some techniques to obtain different 

 colors in granules in the one cell, just as it 

 is possible to stain erythrocytes two dif- 

 ferent colors in the one blood vessel, but 

 such color differences are not significant. 

 Apart from this, there is the possibility, 

 since secretory granules in general contain 

 a mixture of proteins and peptides and not 

 a single substance, that granules vary in 

 quality, due to differing proportions of the 

 several components at different times as a 

 result of different rates of secretion or from 

 other effects. If this is so, differing shades 

 of color may be obtained with some proce- 

 dures in granules containing the same hor- 

 mone. 



E. CHANGES IN CELL PROPORTIONS WITH 

 ALTERATIONS IN FUNCTION 



The modifications in secretory activity, 

 which occur as the result of environmental 

 influences, or after experimental interven- 

 tion, produce in some species distinct dif- 

 ferences in the appearances of stained sec- 

 tions of the pars anterior. These differences 

 are often referred to as "changes in the 

 ]iroportions of chromophil cells." Since in 



many instances such changes in the propor- 

 tions of different cell types occur rapidly 

 and without any proportionate number of 

 mitoses, changes in the proportions of cells 

 have, in the past, been ascribed to the trans- 

 formation of cells of one type into cells of 

 another type. It cannot be said as yet that 

 transformation of one cell type to another 

 does not occur, but, if it does, it must be 

 limited. The impossibility of telling what 

 appearance any given cell would have 

 shown at some time other than the time at 

 which it was taken from the animal pre- 

 cludes a direct examination of transforma- 

 tions. The zonation phenomenon, however, 

 is of the greatest assistance in setting limits 

 to transformations that may occur. The 

 stability of the acidophil and basophil zones 

 in certain mammals shows that basophil 

 cells and the chromophobes of the basophil 

 zone are not transformable into acidophils, 

 nor are acidophils transformable into baso- 

 phils. Moreover, the fact that the anterior 

 lobe hormones have been shown in some 

 species to be not uniformly distributed 

 within the anterior lobe, but to have char- 

 acteristic distributions, different for the dif- 

 ferent hormones, suggests that each hor- 

 mone is the product of a specific cell type 

 not transformable into cells with a different 

 function. 



If, therefore, basophils cannot be trans- 

 formed into acidophils or acidophils into 

 l^asophils, if for the most part each hormone 

 is produced by its own specific cell type 

 which is not transformable into another 

 type with a different function, how can the 

 apparent difference in the proportions of 

 acidoi^hils, basophils, and chromophobes be 

 explained? Three effects are operative. First, 

 in many species a large proportion of the 

 cells of the pars anterior are classified as 

 chromophobes. Most of these cells are cells 

 in a temporarily inactive phase and contain 

 either no specific granulation or granulation 

 in amounts too small to give decided stain- 

 ing reactions. With an alteration in secre- 

 tion rate large numbers of chromophobe 

 cells may accumulate granules. The trans- 

 formation, however, is only from a specific 

 cell low in granule content to one with high 

 granule content, and not the production of 

 a specific cell type from an undifferentiated 

 cell. Second, the size of individual cells 



