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SCIENCE 



[N. S. Vol. XXXIV. No. 888 



chemical way. The secretin which they 

 produce is comparable to an internal se- 

 cretion, since it is turned into the blood 

 and stimulates the pancreas to perform 

 its function; the enteroldnase, on the other 

 hand, is comparable to an external secre- 

 tion since it is turned into the intestinal 

 cavity and thereby activates one of the im- 

 portant constituents of the pancreatic se- 

 cretion. 



An interesting cooperative cycle is ap- 

 parently established around the duodenum. 

 In the stomach, pepsinogen is secreted by 

 certain cells in the gastric glands ; this pre- 

 sumably is activated to pepsin by the 

 hydrochloric acid formed by another type 

 of cell in the gastric glands. The gastric 

 chyme with its hydrochloric acid, on reach- 

 ing the duodenum, stimulates the produc- 

 tion of secretin, which in turn stimulates 

 the flow of the pancreatic juice. The pan- 

 creatic secretion on reaching the duodenum 

 induces the production of enterokinase by 

 which its trypsinogen is activated to 

 trypsin. 



Because of the considerable amount of 

 carbohydrate in the diet, it might natu- 

 rally be expected to find a vigorous dias- 

 tatic enzyme in the saliva of the horse, if 

 in any animal. Yet the saliva taken from 

 the duct of the parotid gland is unable to 

 convert a starch mixture into a reducing 

 sugar except to a very limited extent and 

 after a considerable period of time. Is 

 there an absence of the diastatic enzyme, 

 except such as may filter through to the 

 secretion from the blood, or is there an 

 inert ptyalinogen which meets its activator 

 further down the tract and is there con- 

 verted into the active ptyalin? 



Other examples of cooperation may be 

 mentioned in connection with the pituitary 

 body of the brain, and the thyroid and 

 suprarenal glands. Although not pro- 

 vided with ducts, an internal secretion is 



nevertheless formed which is turned into 

 the blood and lymph and exerts an influ- 

 ence upon the other tissues of the body so 

 important that if the glands become dis- 

 eased or removed, serious or fatal conse- 

 quences result. 



One of the most interesting examples of 

 an internal secretion which is not necessary 

 to life but which yet profoundly affects the 

 chemical changes occurring in the body is 

 that of the ovaries. It has long been fa- 

 miliar to stockmen and others that the re- 

 moval of the ovaries increases consider- 

 ably the rapidity with which fat is laid on. 

 According to the researches of Loewy and 

 Eichter of Berlin the explanation is that 

 the ovaries produce a substance which 

 hastens the oxidation of the tissues and 

 the food. When this substance is injected 

 under the skin of animals in which the 

 ovaries have been removed, the tissue 

 waste is markedly increased. 



Since physiology is concerned with liv- 

 ing matter and that alone, the border lines 

 between it and other biological sciences 

 must of necessity be indefinite and more or 

 less overlapping. This is peculiarly true as 

 to its relation with pathology, medicine 

 and therapeutics. The chief function of 

 the living tissues is change — metabolism. 

 Changes of composition, form or even 

 structure are pertinent to physiology if 

 they occur in the living tissue. The activ- 

 ity of the tissues may be increased or de- 

 creased for a greater or less time and the 

 conditions still remain within normal lim- 

 its. There may be a lack of cooperation 

 for a time without abnormal results. The 

 dividing line between the normal and the 

 abnormal is at the outset imperceptible. 

 Bacteria are present in the normal body 

 and are more or less concerned with the 

 normal functions of the alimentary tract. 



Physiology stands for cooperation, 

 pathology deals with a disturbed coopera- 



