482 SECRETION. 



causative relation to the discoloration or to the constitutional disturbance. It is more 

 interesting to us, however, to know that the investigations into these diseased conditions 

 have developed little or nothing of importance concerning the physiology of the supra- 

 renal capsules. 



Extirpation of the Suprarenal Capsules. There are two important questions to be 

 settled by the removal of the suprarenal capsules from living animals. The first is, 

 whether or not these organs are essential to life ; and the second, to determine the con- 

 sequences of their removal, as exhibited in modifications of the animal functions. 



Are the suprarenal capsules essential to life ? This question can be answered in a very 

 few words. Dr. Brown-Sequard, in his first experiments, removed sometimes one and 

 sometimes both capsules in rabbits, Guinea-pigs, dogs, and cats, and the animals died in 

 the course of two or three days. He also noted several peculiar results, such as turning, 

 and contraction of the pupil, when one capsule had been extirpated, and the development 

 of peculiar crystals in the blood. M. Gratiolet repeated these experiments and ascertained 

 that the left capsule could be removed with impunity, while extirpation of the right was 

 always fatal. M. Philipeaux added a number of observations, experimenting chiefly upon 

 rats and taking great care to disturb the adjacent organs as little as possible. As the result 

 of these experiments, he concluded that the capsules are not essential to life. Of four rats 

 operated upon in this way, three died, as Philipeaux supposed, of cold, the first in nine 

 days, the second in twenty-three days, and the third in thirty-four days. One was alive 

 and well when the report was made, although the capsules had been removed for forty- 

 nine days. In such a question as this, negative experiments are of little account ; and the 

 instances in which animals have recovered and lived perfectly well after removal of both 

 suprarenal capsules show conclusively that they are not essential to life. Death has prob- 

 ably been due, in most of the experiments, to injury of the semilunar ganglia, and it is 

 probably on account of the greater injury, from the situation of the capsule, produced 

 by operating on the right side, that the removal of the capsule of that side has been more 

 generally fatal. It is not necessary to take account, in this connection, of the contraction 

 of the pupil, "turning" and other symptoms referable to the nervous system, which have 

 sometimes followed these operations. These phenomena are undoubtedly due to injury 

 of adjacent parts, and not to extirpation of the capsules. The only remaining question to 

 determine is whether the capsules have any thing to do with the formation or change of 

 pigment. Notwithstanding the assertion of Dr. Brown-Sequard, that flakes of pigment 

 and blood-crystals differing from those developed in normal blood are found in animals 

 deprived of the suprarenal capsules, this view is adopted by a few physiological authori- 

 ties. In view of these facts, and in the absence of comparative examinations of the blood 

 going to the suprarenal capsules by the arteries and returned from them by the veins, it 

 is impossible to assign any definite function to these bodies, and it is certain that they 

 are not essential to life. Their greater relative size before birth has led to the supposi- 

 tion that they might have an important office in intra-uterine life, but this is a pure 

 hypothesis, based upon no positive knowledge. 



Thyroid Gland. 



The history of this gland belongs almost exclusively to descriptive anatomy, and its 

 only physiological interest is in the similarity of its structure to that of the other ductless 

 glands. It has no excretory duct. It is attached to the lower part of the larynx, follow- 

 ing it in its various movements. Its color is brownish-red. The anterior face is convex 

 and is covered by certain of the muscles of the neck. The posterior surface is concave 

 and is applied to the larynx and trachea. It is formed of two lateral lobes, with a 

 rounded, thickened base below, and a long, pointed extremity extending upward, con- 

 nected by an isthmus. Each of these lobes is about two inches in length, three-quarters 

 of an inch in breadth, and about the same in thickness at its thickest portion. The isth- 



