MR. E. C. BABER OR THE STRUCTURE OF THE THYROID GLAND. 
595 
already described as passing into the vesicles of the Dog’s thyroid gland ; but from a 
comparison of them with the fresh blood of the Tortoise, and from the occurrence of very 
similar cells in the blood-vessels in sections of the hardened gland of the same animal, 
I think there can be no doubt that they are colourless blood-corpuscles. It is scarcely 
necessary to mention that these cells can be easily distinguished from any post-mortem 
tailing in of the epithelial cells ; moreover, in these specimens the epithelium was 
usually intact. In specimens prepared in osmic acid these cells come out very clearly, 
and their cell-substance presents a coarsely-granular appearance. 
Some of these Tortoises were killed by decapitation, after a ligature had been tightly 
tied round the neck, but the method of killing could have had no effect in causing the 
escape of these cells, for they were found equally in those killed by simple decapi¬ 
tation without ligature. The appearances observed also left no doubt that they had 
entered the vesicles during' the life of the animal. 
A few large nucleated cells have been observed in the vesicles of the thyroid gland 
of the Rook, which were probably colourless blood-corpuscles. 
In one thyroid gland of a Dog (aged 9 weeks), many vesicles contained a quantity 
of cells with granular cell-substance and indistinct outline, both in them cavity and 
in the substance of the epithelial wall. The nuclei of these cells were smaller, and 
stained more deeply with hmmatoxylin than those of the epithelial cells. These cells, 
which I conclude were colourless blood-corpuscles, I am inclined to regard as a patho¬ 
logical appearance, as they were only seen in part of one gland of this Puppy. 
Their occurrence in the vesicles cannot therefore be compared with the migration of 
colourless corpuscles into the vesicles of the Tortoise, which from its being constantly 
present is doubtless a normal phenomenon. 
It appears, therefore, that a migration of colourless blood-corpuscles into the vesicles 
is a physiological occurrence in the thyroid gland of the Tortoise, but that it may also 
occur in other animals. 
( d) Rounded masses, embedded in the homogeneous material, have been observed 
in various animals. These are usually homogeneous in character, with smooth, or 
sometimes jagged outline, and stain darkly with hsematoxylin (more so than the sur¬ 
rounding homogeneous substance), or of a bright yellow colour with picrocarminate 
of ammonia. They have been observed in the thyroids of Dog, Rook, Fowl, Pigeon, 
Conger Eel, and Skate. In the latter they sometimes presented the following 
appearance. The central portion was deeply stained with hmmatoxylin, whilst the 
periphery remained almost colourless. Whether these are pathological in character 
or not, and what relation they bear to the homogeneous contents of the vesicle, I am 
unable to say. 
(e) Crystals were found in the homogeneous material in the gland-vesicles of the 
Tortoise and Rook, the latter being the bird in which it w 7 as concluded (as above- 
described, p. 593) that hoemorrhage had taken place into almost all the vesicles. The 
crystals in this case were present in considerable numbers. 
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