422 



SCIENCE PROGRESS 



powered by the pressor, while with subsequent injections these 

 conditions are generally reversed (31). 



Besides the pressor and depressor constituents of extract of 

 the infundibular part of the pituitary body, this organ yields a 

 substance soluble in water and not destroyed by boiling, which 

 acts specifically upon the kidney, producing, along with dila- 

 tation of the renal vessels, an increase of secretion from the 

 tubules. According to Schafer and Herring (32), the diuretic 

 activity of the substance formed by and contained within the 

 gland is greater than that of any diuretic in the pharmacopoeia ; 

 and assuming that the pituitary is an internally secreting gland, 

 it is probable that the main purpose of its secretion is ancillary 

 to the function of the renal organs. 



Extracts of the posterior lobe of the pituitary body of the ox 

 produce a distinct dilatation of the pupil of the enucleated frog's 



eye (33)- 



It is to be noted particularly that all these effects are 

 obtained from the posterior — the " nervous " — part of the 

 pituitary; and the pituitary of the elasmobranch fishes, which 

 has no nervous portion, does not yield active extracts (34). 



(c) Theories as to the functions of the pituitary body. — The 

 theory held by Schafer and Herring is that the internal 

 secretion of the nervous part of the gland controls the renal 

 functions, both by the effects of its secretion upon the vascular 

 system in general, as well as by a direct influence exerted by 

 one of its constituents upon the renal cells and upon the renal 

 circulation in particular. 



It has been supposed that the pituitary may act vicariously 

 for the thyroid gland. 



The condition of acromegaly is frequently found to be 

 associated with tumours of the pituitary body ; and it is inte- 

 resting, as pointed out by Schafer and Herring, that cases of 

 tumour of the pituitary have been recorded in which polyuria 

 was a prominent symptom. 



(iv) The Thymus Gland 



The thymus gland may be classed in a general way with the 

 lymphoid tissues. It is well developed in late fcetal life and in 

 the new-born, and reaches its highest development about the 

 end of the second year, although it occasionally retains a con- 

 siderable size in the adult. After the second year it atrophies 



