416 Dynamic Theory. 



CHAPTER XLIII. 



EFFECTS OF LIGHT AND HEAT ON ORGANISMS. 



We will now turn our attention more particularly to the effects of light, 

 heat and other dynamic agencies upon animal races in general, and our 

 own in particular, in the production of special phases of development, 

 in the creation of special functions and the erection by their means of 

 special organs ; most notably, organs of sense and organs of reflexion, 

 whereby the impact of the forces upon the body is caused to reappear in 

 new forms of motion. As shown in chapter 41, it is the waves that are 

 pitched in unison with the periods of the fundamentals of the molecular 

 spaces of the body that set up vibrations in the body and so cause it to 

 do work. So, the action of those waves not in complete unison, tends to 

 so differentiate the molecules with which they come into contact as to 

 perfect the unison, and get the body gradually into a condition to be 

 easily set in motion by the impact of the waves of force. This is the 

 essence of the habit that has been insisted upon as the great differentiat- 

 ing agency in organic development. The organism is a plastic mass 

 and may within certain limits be moulded to unison with various tones 

 of the impinging force if only time be given and the force be uniform. 

 We have seen that both of these conditions have been supplied, and as 

 a result we see organs differentiated to sympathy with certain vibrations 

 of ethereal energy. Something has been said of these in former chap- 

 ters, but they will receive more particular attention in the chapters to 

 come. 



Some of the effects of light on animal organization are of common ob- 

 servation. Sunstroke is now known to be due to light. It may occur in 

 the moderate weather of spring and may be caused by electric light. It 

 is due to the action of the violet and ultra violet rays, and may be pre- 

 vented by the protection of uranium glass which absorbs these ra} r s. 

 ( Papillon. ) Hemicrania, or sun-pain, is a pain of intermittent charac- 

 ter involving only one side of the head and lasting only while the sun is 

 above the horizon. But the effects of light go deeper than the skin, af- 

 fecting the action of all the plastic tissues of the body. f ' Miners and 

 others working in the dark are liable to undue preponderance of the 

 lymphatic system, a susceptibility to catarrh in the mucous membranes, 

 flaccidity of the soft parts, swellings and distortions of the bony system, 

 &c. " On the other hand, people of the tropics who go more or less 

 naked are seldom deformed. Light gives to all the tissues their proper 

 stimulus and the body is developed symmetrically. The fact is that a 

 great part of organic movement is due to the impulses of light. When 

 there is a cessation of these impulses the movement of organic develop- 



