352 RESPIRATION. 



that this accounts for the failure to produce fatal results in rabbits 

 by the removal of the thyroid, the pituitary body being especially 

 well developed in that animal. It is stated by some that acromey- 

 aty) a disease characterized by hypertrophy of the bones of the 

 face and extremities, and also of the skin, is associated with 

 enlargement and degeneration of the pituitary body. Dr. Kinnicutt 

 states that in 34 recorded cases of acromegaly, with full autopsy, 

 a microscopic lesion of the pituitary body has been found in every 

 instance, and in the majority of cases it has proved to be either a 

 simple hyperplasia or a tumor growth of some kind. Others have 

 not found these lesions in cases of enlargement of the gland, but 

 rather a persistence of the thymus. 



There seems to be no valid reason for concluding that the 

 thyroid and the pituitary body have any physiologic relation with 

 each . other. Injections of extracts of the pituitary body cause 

 great increase in the force of the heart's beat, and also an increase 

 in blood-pressure by contracting the arterioles ; that of the thyroid 

 does neither. 



That the pituitary body furnishes an internal secretion seems 

 to be beyond question, and this has the effect of increasing the 

 contraction of the heart and arteries, and also of influencing the 

 metabolism of the bones and nervous system, but just how this is 

 brought about is not determined. 



THE CAROTID AND THE COCCYGEAL GLANDS. 



The carotid gland is situated at the bifurcation of the common 

 carotid artery, and the coccygeal gland or Luschka's gland is 

 situated in front of the tip of the coccyx, just above the attachment 

 of the sphincter ani. These glands are collections of small arteries 

 enclosed in granular polyhedral cells, the whole being enclosed 

 in a capsule. Into the coccygeal gland sympathetic nerves pass. 

 Macalister regards it as consisting of " the condensed and con- 

 voluted metameric dorsal arteries of the caudal segments embedded 

 in tissue which is possibly a small persisting fragment of the 

 neurenteric canal." 



The function of these glands is unknown, if, indeed, they 

 possess any. 



RESPIRATION. 



One of the most important processes carried on in the body is 

 that by which the tissues receive oxygen. In animals whose 

 structure is exceedingly simple, and so constituted that all portions 

 of their bodies are bathed by the oxygen-carrying medium, the 

 oxygen is directly absorbed ; but in those in which there are 

 tissues remotely situated as regards this medium, some provision 

 must be made for conveying the oxygen from the medium to the 



