io FIRST PRINCIPLES. 



except that before the tar was put on, he got a thick 

 preliminary coating of glue, succumbed in nine hours. In 

 all these cases the symptoms were those of gradual suffo- 

 cation (gradual cutaneous asphyxia, as Bouley termed it), 

 namely, the breathing became slow and deep, and the 

 pulse weaker and weaker; the mucous membranes of the 

 eyelids and nostrils assumed a purple hue ; and the body 

 and expired air became colder and colder. Bouley's con- 

 clusions on the subject appear to have been confirmed by 

 the experiments of Colin, Becquerel, and others. Against this 

 view, some physiologists (see Kirkes' Physiology) argue that 

 such cases of death are caused by cold and not by asphyxia. 

 As, however, they admit that this varnishing of the skin does 

 not seem dangerous to human beings, and as men are far more 

 susceptible to a low temperature than horses ; it may not 

 be unreasonable to conclude that Bouley and his followers 

 were right, and that the skin of the horse exhales a larger 

 quantity of carbonic acid than that of man. In any case, 

 experience shows that when the nature of the work done by 

 a horse, imposes a severe strain on his lungs, we should do 

 our utmost to keep his skin in good working order. 



In the discharge of water from the system, we have an 

 admirable instance of reciprocal action ; for in cold weather 

 when the skin is inactive, far more urine is passed by the 

 kidneys, than in hot weather when the skin is in full work. 



The skin aids to a small extent in the excretion of urea, 

 which, on reaching the surface, becomes rapidly converted into 

 carbonate of ammonia (p. 46). 



ENERGY IN PLANTS AND ANIMALS. 



The scientific meaning of energy is the capacity of doing 

 work ; and work may be defined as the movement of weight. 

 Thus, a unit of work is reckoned as a weight of one pound 

 raised through a space of one foot. 



