Remarks on Impulses Cerebral and Spinal. 535 



maximum at 0", and at 30° in rapid heating-. The duration of the 

 contraction increases with diminution of the weight, increase of stimulus, 

 and when the temperature diminishes. The tonic contraction of the 

 snail's heart disappears with a rising temperature but returns with 

 cooling. Light, and other stimuli, induce changes in plant cells. The 

 leaflets that have drooped owing to darkness are restored by light, 

 which is known to bring about chemical changes in inanimate, as well 

 as animate, nature. The pigmentation of the skin in animals and the 

 green colour of plants are amongst its operations. It may be remem- 

 bered that Eichet, Chauveau, W. His (jun.), Pompilian, Gad, Bernstein, 

 Grünhagen and Samkowy, Marey and Franck, and Weiss, have done 

 much work to place our knowledge on a sure foundation in the above 

 regard. Electrical phenomena in plants and animals owe much to 

 Du Bois-Eeymond, Burdon-Saunderson and Gotch. Nerve work hurries 

 up the phenomena of muscle contraction and the vagus appears to 

 have indirect inhibiting control. Eeflex action brought on by abnormal 

 contraction may act through the branches of the vagus on other parts. 

 Biological units are responsive to one or more forces in nature which 

 they utilize. Plants use by their roots heat, gravity and moisture. 

 Eheotropism, heliotropism, geotropism, hydrotropism and chemiotaxis 

 are expressions meant to indicate the possibilities which are within 

 the plant organism. 



"Science is presented to us" says Kelvin, "not as an entgötterte 

 Natur" — it is not a God-forsaken, a soul-less nature consisting of 

 force and light, chemicals and crystals, deprived of thoughts of God, 

 deprived of life, which Science contemplates". "Science brings us to 

 the threshold of life, and it knows its own incapacities to subject life 

 to the laws of force and electricity." The attempt of biological units 

 to appreciate biological units is attended with advantage, it is what 

 is called by medical men, in reference to touch, the tadus eruditus. 

 This may, perhaps, be described as an attempt by an artistic method 

 to learn a great many things in a composite form for comparison. 

 Biological units avail themselves of the energy in nature, and save 

 their own energy, themselves, and their race. If they fail to do this, 

 and to adapt themselves they are lost. Darwin and Wallace made 



