SOURCES OF ANIMAL HEAT. 19 1 



the most sedulous attention is paid to the purity of 

 the air in which they live. 



The necessity for adequate ventilation is nowhere 

 more urgent than in many of our manufactories, 

 where, from the length of time (varying from 10 to 

 17 hours a day) during which the operatives are 

 exposed to the evils of impure air, a great sacrifice 

 ^ of health and happiness is constantly going on- The 

 ' dust floating in the air in cotton manufactories and 

 spinning-mills, and produced in many trades, is a 

 very serious aggravation of their situation, as all 

 foreign bodies thus inhaled into the lungs produce 

 irritation in their structure, and sooner or later lead 

 to the development of fatal pulmonary disease. 



In the third chapter, I pointed out the necessity 

 of protecting the skin by suitable clothing, and men 

 tioned the intimate relation which subsists between 

 its function and those of the lungs. We have now 

 to consider this subject a little further, as regards 

 the origin and regulation of the animal heat. 



The true sources of animal heat are still imper- 

 fectly known, and any discussion concerning them 

 would be too abstract for the present volume. Its 

 regular production, however, is an essential condition 

 of life. If the human body did not possess within 

 itself the power of generating heat, so as to maintain 

 nearly an equality of temperature in all climates, it 

 could not long exist. In winter, and especially in 

 the northern regions, the blood would speedily be 

 converted into a solid mass, and life be extinguished, 

 if no provision existed for replacing the caloric 

 withdrawn from the system by the surrounding cold. 

 In most parts of the globe, the heat of the atmo- 

 sphere is, even in summer, inferior to that of the 

 human body, and consequently a loss of caloric is 

 always going on, which must be made up in some 

 way,* other wise disease and death would speedily 

 ensue. In cholera a very remarkable diminution of 



