SECRETION. 249 



In a very interesting research by Bruno 1 it has been shown that the 

 actual passage of bile into the intestine is occasioned, reflexly no <1< ml >t , by 



the passage of the chyme from stomach to intestine. As long as the stomach 

 is empty no bile flows into the duodenum ; the flow commences when the 

 stomach begins to empty its contents into the intestine, and ceases as soon as 

 this process is completed. The author endeavored to ascertain the substances 

 in the chyme that serve as the stimulus in this reaction. As far as his experi- 

 ments go, they show that fats and the digested products of proteids (peptones 

 and proteoses) are the most efficient stimuli. Acids, alkalies, and starch or 

 the substances formed from it during salivary digestion are ineffective. Pre- 

 sumably the fats and the products of proteid digestion act on the sensory 

 fibres of the duodenal membrane. 



Effect of Complete Occlusion of the Bile-duct. — It is an interesting 

 fact that when the flow of bile is completely prevented by ligation of the bile- 

 duct, the stagnant liquid is not reabsorbed by the blood directly, but by the 

 lymphatics of the liver. The bile-pigments and bile-acids in such cases may 

 be detected in the lymph as it flows from the thoracic duct. In this way they 

 get into the blood, producing a jaundiced condition. The way in which the 

 bile gets from the bile-ducts into the hepatic lymphatics is not definitelv known, 

 but possibly it is due to a rupture, caused by the increased pressure, at some 

 point in the course of the delicate bile-capillaries. 



Kidney. 



Histology. — The kidney is a compound tubular gland. The constituent 

 uriniferous tubules composing it may be roughly separated into a secreting 

 part comprising the capsule, convoluted tubes, and loop of Henle, and a col- 

 lecting part, the so-called straight collecting-tube, the epithelium of which is 

 assumed not to have any secretory function. Within the secreting part the 

 epithelium differs greatly in character in different regions; its peculiarities 

 may be referred to briefly here so far as they seem to have a physiological 

 bearing, although for a complete description reference must he made to some 

 work on Histology. 



The arrangement of the glandular epithelium in the capsule with reference 

 to the blood-vessels of the glomerulus is worthy of special attention. It will 

 be remembered that each Malpighian corpuscle consists of two principal parts, 

 a tuft of blood-vessels, the glomerulus, and an enveloping expansion of the 

 uriniferous tubule, the capsule. The glomerulus is a remarkable structure (set- 

 Fig. 65, ^1). It consists of a small afferent artery which after entering the 

 glomerulus breaks up into a number of capillaries, which, though twisted 

 together, do not anastomose. These capillaries unite to form a single efferent 

 vein of a smaller diameter than the afferent artery. The whole structure, 

 therefore, is not an ordinary capillary area, but a rete mirabile, and the phys- 

 ical factors are such that within the capillaries of the rete there must he a 

 greatly diminished velocity of the blood-stream, owing to the great increase 

 1 Archives des sciences biologiques, 18'J9, t. vii. p. 87. 



