INTRODUCTORY PROBLEMS 7 



There are so many excellent introductions to the study of 

 physiology, of which Huxley's Elementary Lessons remains best, 

 that we need not expand this section. It is very important 

 that the pupils should be helped to clear ideas in regard to the 

 everyday functions of contractility, irritability, nutrition, respir- 

 ation, and excretion, and there are many simple and innocent 

 practical experiments which are of use. It is not much that the 

 pupil should blow his breath into lime water, and by seeing it 

 become cloudy, infer that he breathes out carbon dioxide, but it 

 is of more value than many definitions of respiration. It is 

 instructive to show artificial digestion in a test-tube, to demon- 

 strate that it may mean making a very solid piece of food fluid 

 and diffusible, and to show that the same occurs on the leaf of the 

 butterwort on the moor. The teacher should show at least a 

 dozen of these simple experiments before he allows the pupils 

 to speak of " the functions of the animal body." 



The Physical Basis of these Activities. When we take an animal 

 to pieces we find, unless it be one of the very simple animals, 

 that it consists of numerous organs such as brain, heart, stomach, 

 and so on. Penetrating somewhat deeper, we find that these 

 organs are built up of various kinds of tissue, nervous, muscular, 

 glandular, connective, and the like. But a tissue is composed of 

 numerous similar unit-corpuscles or unit-areas of living matter 

 the cells, and each cell is a little world in itself. If we compare an 

 animal to a city, an organ is like a region of the city given over 

 to some particular occupation or industry, here a block of govern- 

 ment offices, and there a manufacturing quarter ; a tissue is 

 comparable to a street of similar houses or workshops ; a cell 

 is an individual house or workshop, and the inhabitants or 

 workers are the particles of living matter. The history of the 

 science shows that there has been a gradually deepening analysis, 

 though research at every level still continues, and must for a very 

 long time continue. 



The physiologist who studies vital activity must pass from 

 his observation of the animal as a unity with certain habits, 

 to consider it in succession as an engine of organs, as a web of 

 tissues, as a city of cells, and as a whirlpool of living matter. 



School studies, recapitulating the history of the science, 



