46 R. R. BENSLEY 



tents, rather irregular in shape, occurring in the base of the cell, 

 and with the frequent occurrence in the cells of hyperplastic 

 human glands from cases of true exophthalmic goiter of droplets 

 of material staining like colloid located similarly in the extreme 

 bases of the cell near the capillary net. Ferguson ('11), also, 

 has described the occasional occurrence in the thyroid gland of 

 elasmobranch fishes of cells presenting in their basal ends a 

 ragged and rodded appearance which he interprets as due to 

 secretion storage for direct export to the vascular channels. 



A group of opossums kept un.der observation under various 

 experimental conditions during the past winter have furnished 

 material in which, by reason of the fact that these vacuolar sub- 

 stances in the cell were unusually increased in amount, it was 

 possible to study their variation and to develop a technique for 

 staining of their contents. One group of these animals was kept 

 for a period of three weeks on a dietary consisting of beef, bread 

 and fat, egg, bread and fat, or cheese, bread and fat, just suffi- 

 cient to maintain constant weight. In another group the diet 

 was so regulated that with constant bread and fat content there 

 was a progressive increment of meat fed to the successive mem- 

 bers of the series. In all of the animals thus kept on a controlled 

 diet, the thyroid cells contained such basal vacuoles, and in two 

 of the animals of the second series, namely those which received, 

 respectively, twice and two and a half times the normal meat 

 ration, the material of this sort comprised fully half of the cell 

 contents. 



The fixation of the material is of considerable importance in 

 the study of these vacuolar substances, because the contents 

 are so dilute that they may be precipitated in an invisible form 

 on the protoplasmic strands which wall the vacuoles. Formalin 

 Zenker, how^ever, was found to precipitate the contents in the form 

 of a thin gel sometimes filling completely the space of the vacu- 

 oles, sometimes containing small vacuoles from contraction in 

 fixation. Staining however was difficult, because the material 

 stained with the usual dyes in the same way as the protoplasm. 

 With Mallory's connective tissue stain, however, it could be seen 

 that the vacuoles had vaguely staining contents, but, since the 



