As a result of recent studies on secretory synthesis, the following conclusions have been reached :
1. Many gland-cells run through a regular ‘secretory cycle’, beginning with a small cell devoid of secretory granules, progressing through a period in which large numbers of granules are produced and terminating in an act of extrusion of the granules. The cycle may or may not be repeated according to the nature of the cell.
2. The Golgi apparatus is from the beginning present in all kinds of secretory cells, and during the secretory cycle becomes very greatly hypertrophied, establishing a volume in rough relation to that of the secretory products.
3. The topography and behaviour of the apparatus is different in different kinds of glands, but is roughly divisible into three general types characteristic of cells which produce serous, mucous, and lipoidal secretions.
4. The secretory granules make their first appearance only within the area delimited by the Golgi apparatus.
5. In a few cases relations have been made out which indicate that the secretory granules arise in close connexion with the Golgi material.
6. It is concluded that secretory granules are differentiated by the Golgi material, but that no direct transformation of the one into the other occurs such as was claimed by some authors in the case of the mitochondria.
7. It is suggested that the Golgi material is structurally homologous throughout the range of animal cells, and that the so-called idiosomic substance, sometimes associated with it, is to be looked upon as one phase of a duplex system in which the relative development of lipoidal and idiosomic substances may undergo considerable variation.
8. It is suggested that the relation between the Golgi apparatus and secretory granules is homologous to that existing between the Golgi apparatus and the developing acrosome of the animal sperm, and that our rather complete under standing of the latter phenomenon can thus be used as a basis for interpreting the much more obscure phenomena in the gland-cell.
9. No cytological evidence of the origin of secretory products from the nucleus receives any general acceptance at the present time. The nucleus can be considered as the source of secretions only in the indirect sense that it may possibly exercise some control over the process as a whole or may collaborate with other parts of the cell system in preparing materials for the actual synthetic operations of the Golgi apparatus.
10. The establishment of the views here developed must depend finally upon further critical evidence bearing upon the exact relation which exists between individual secretory granules and the Golgi complex.