^ May, 1908.] Ele?nents of Animal Physiology. 263 



buy it would mean to the owners of cattle and sheep who live above and 

 beyond the canals. If we had begun this season with 25,000 acres of lucerne 

 meadow the hay from it would have made the owners the stock men's 

 bankers for the next five years. What is true of this year will be true of 

 regularly recurring years so long as this continent endures. 



In order to grow hay on a large scale we must have improved tools. 

 No work is harder than making hay by human muscle. I know, because 

 as a boy I cut many acres of hay with a scythe. On the other hand, no 

 farm work is easier or more agreeable than making hay by machinerv. I 

 know that also from trial. American inventors have done almost as much 

 fo cheapen and lighten hay-making as Australian inventors have done to 

 -cheapen and lighten the labour of harvesting grain. The purpose of the 

 accompanying illustrations is to show more clearly than anv description 

 could the appearance of modern hay-making tools and the method of their 

 •operation. 



THE ELEMENTS OF ANIMAL PHYSIOLOGY. 



W. A. Oshonic. M.B.. D.Sc. Professor of Pliysiology and Histologv, 

 Dean of tlie Faeulty of Agriculiurc in tlie Universitv of Melbourne. ' 



{Conlinned from Page 764, Vol. T.) 



X. Digestion and Absorption {contimced.) 



DIGESTION IN THE SMALL INTESTINES.— In the duodenum 

 the food mass or chyme as it is called, encounters the pancreatic juice and 

 the bile, concerning the secretion of which a few words may be now said. 

 In the wall of the duodenum is a substance called prosecretin, which is held 

 fast by the epithelial cells. When, however, this substance comes into con- 

 tact with an acid it is changed into another bodv called secretin which is 

 liberated by the cell, is caught up by the blood stream and so reaches 

 eventually all parts of the body. Now secretin is a true hormone or 

 ■chemical messenger, for it acts on the pancreas causing this to secrete 

 pancreatic juice; it also acts on the liver causing this to secrete bile; and 

 it probably acts on the duodenal tubular glands causing these to secrete 

 succus entericns. The mechanism is therefore simple. The stomach content 

 or chyme is acid ; it liberates therefore secretin ; the pancreas and liver are 

 •stimulated therefore to secrete and, as their secretions are alkaline, it 

 follows that they will continue to be stimulated until the acid of the 

 chyme is neutralized ; when this happens no more secretin will be formed 

 and the activity of the pancreas and the liver will come to a halt. But 

 when a fresh squirt of chyme is sent into the duodenum the same cvcle 

 will start over again. 



The pancreatic juice is in many respects the most important digestive 

 ■secretion in the body. It contains the following ingredients besides 

 water and a little protein: — 



1. sodium carbonate, about 0.6 per cent., which neutralises the acid 



of the chyme, emulsifies the fats and oils and to which the 

 alkalinitv of the juice is due, 



2. lipase, called also steapsiii which splits fats into fatty acids and 



glycerine. 



